xref: /libCEED/rust/libceed/src/qfunction.rs (revision 1142270cb02df4484c0ba89e11097db6aa2d5cef)

// Copyright (c) 2017, Lawrence Livermore National Security, LLC. Produced at
// the Lawrence Livermore National Laboratory. LLNL-CODE-734707. All Rights
// reserved. See files LICENSE and NOTICE for details.
//
// This file is part of CEED, a collection of benchmarks, miniapps, software
// libraries and APIs for efficient high-order finite element and spectral
// element discretizations for exascale applications. For more information and
// source code availability see http://github.com/ceed.
//
// The CEED research is supported by the Exascale Computing Project 17-SC-20-SC,
// a collaborative effort of two U.S. Department of Energy organizations (Office
// of Science and the National Nuclear Security Administration) responsible for
// the planning and preparation of a capable exascale ecosystem, including
// software, applications, hardware, advanced system engineering and early
// testbed platforms, in support of the nation's exascale computing imperative

//! A Ceed QFunction represents the spatial terms of the point-wise functions
//! describing the physics at the quadrature points.

use std::pin::Pin;

use crate::prelude::*;

pub type QFunctionInputs<'a> = [&'a [crate::Scalar]; MAX_QFUNCTION_FIELDS];
pub type QFunctionOutputs<'a> = [&'a mut [crate::Scalar]; MAX_QFUNCTION_FIELDS];

// -----------------------------------------------------------------------------
// CeedQFunction option
// -----------------------------------------------------------------------------
pub enum QFunctionOpt<'a> {
    SomeQFunction(&'a QFunction<'a>),
    SomeQFunctionByName(&'a QFunctionByName<'a>),
    None,
}

/// Construct a QFunctionOpt reference from a QFunction reference
impl<'a> From<&'a QFunction<'_>> for QFunctionOpt<'a> {
    fn from(qfunc: &'a QFunction) -> Self {
        debug_assert!(qfunc.qf_core.ptr != unsafe { bind_ceed::CEED_QFUNCTION_NONE });
        Self::SomeQFunction(qfunc)
    }
}

/// Construct a QFunctionOpt reference from a QFunction by Name reference
impl<'a> From<&'a QFunctionByName<'_>> for QFunctionOpt<'a> {
    fn from(qfunc: &'a QFunctionByName) -> Self {
        debug_assert!(qfunc.qf_core.ptr != unsafe { bind_ceed::CEED_QFUNCTION_NONE });
        Self::SomeQFunctionByName(qfunc)
    }
}

impl<'a> QFunctionOpt<'a> {
    /// Transform a Rust libCEED QFunctionOpt into C libCEED CeedQFunction
    pub(crate) fn to_raw(self) -> bind_ceed::CeedQFunction {
        match self {
            Self::SomeQFunction(qfunc) => qfunc.qf_core.ptr,
            Self::SomeQFunctionByName(qfunc) => qfunc.qf_core.ptr,
            Self::None => unsafe { bind_ceed::CEED_QFUNCTION_NONE },
        }
    }

    /// Check if a QFunctionOpt is Some
    ///
    /// ```
    /// # use libceed::prelude::*;
    /// # fn main() -> Result<(), libceed::CeedError> {
    /// # let ceed = libceed::Ceed::default_init();
    /// let mut user_f = |[u, weights, ..]: QFunctionInputs, [v, ..]: QFunctionOutputs| {
    ///     // Iterate over quadrature points
    ///     v.iter_mut()
    ///         .zip(u.iter().zip(weights.iter()))
    ///         .for_each(|(v, (u, w))| *v = u * w);
    ///
    ///     // Return clean error code
    ///     0
    /// };
    ///
    /// let qf = ceed
    ///     .q_function_interior(1, Box::new(user_f))?
    ///     .input("u", 1, EvalMode::Interp)?
    ///     .input("weights", 1, EvalMode::Weight)?
    ///     .output("v", 1, EvalMode::Interp)?;
    /// let qf_opt = QFunctionOpt::from(&qf);
    /// assert!(qf_opt.is_some(), "Incorrect QFunctionOpt");
    ///
    /// let qf = ceed.q_function_interior_by_name("Mass1DBuild")?;
    /// let qf_opt = QFunctionOpt::from(&qf);
    /// assert!(qf_opt.is_some(), "Incorrect QFunctionOpt");
    ///
    /// let qf_opt = QFunctionOpt::None;
    /// assert!(!qf_opt.is_some(), "Incorrect QFunctionOpt");
    /// # Ok(())
    /// # }
    /// ```
    pub fn is_some(&self) -> bool {
        match self {
            Self::SomeQFunction(_) => true,
            Self::SomeQFunctionByName(_) => true,
            Self::None => false,
        }
    }

    /// Check if a QFunctionOpt is SomeQFunction
    ///
    /// ```
    /// # use libceed::prelude::*;
    /// # fn main() -> Result<(), libceed::CeedError> {
    /// # let ceed = libceed::Ceed::default_init();
    /// let mut user_f = |[u, weights, ..]: QFunctionInputs, [v, ..]: QFunctionOutputs| {
    ///     // Iterate over quadrature points
    ///     v.iter_mut()
    ///         .zip(u.iter().zip(weights.iter()))
    ///         .for_each(|(v, (u, w))| *v = u * w);
    ///
    ///     // Return clean error code
    ///     0
    /// };
    ///
    /// let qf = ceed
    ///     .q_function_interior(1, Box::new(user_f))?
    ///     .input("u", 1, EvalMode::Interp)?
    ///     .input("weights", 1, EvalMode::Weight)?
    ///     .output("v", 1, EvalMode::Interp)?;
    /// let qf_opt = QFunctionOpt::from(&qf);
    /// assert!(qf_opt.is_some_q_function(), "Incorrect QFunctionOpt");
    ///
    /// let qf = ceed.q_function_interior_by_name("Mass1DBuild")?;
    /// let qf_opt = QFunctionOpt::from(&qf);
    /// assert!(!qf_opt.is_some_q_function(), "Incorrect QFunctionOpt");
    ///
    /// let qf_opt = QFunctionOpt::None;
    /// assert!(!qf_opt.is_some_q_function(), "Incorrect QFunctionOpt");
    /// # Ok(())
    /// # }
    /// ```
    pub fn is_some_q_function(&self) -> bool {
        match self {
            Self::SomeQFunction(_) => true,
            Self::SomeQFunctionByName(_) => false,
            Self::None => false,
        }
    }

    /// Check if a QFunctionOpt is SomeQFunctionByName
    ///
    /// ```
    /// # use libceed::prelude::*;
    /// # fn main() -> Result<(), libceed::CeedError> {
    /// # let ceed = libceed::Ceed::default_init();
    /// let mut user_f = |[u, weights, ..]: QFunctionInputs, [v, ..]: QFunctionOutputs| {
    ///     // Iterate over quadrature points
    ///     v.iter_mut()
    ///         .zip(u.iter().zip(weights.iter()))
    ///         .for_each(|(v, (u, w))| *v = u * w);
    ///
    ///     // Return clean error code
    ///     0
    /// };
    ///
    /// let qf = ceed
    ///     .q_function_interior(1, Box::new(user_f))?
    ///     .input("u", 1, EvalMode::Interp)?
    ///     .input("weights", 1, EvalMode::Weight)?
    ///     .output("v", 1, EvalMode::Interp)?;
    /// let qf_opt = QFunctionOpt::from(&qf);
    /// assert!(
    ///     !qf_opt.is_some_q_function_by_name(),
    ///     "Incorrect QFunctionOpt"
    /// );
    ///
    /// let qf = ceed.q_function_interior_by_name("Mass1DBuild")?;
    /// let qf_opt = QFunctionOpt::from(&qf);
    /// assert!(
    ///     qf_opt.is_some_q_function_by_name(),
    ///     "Incorrect QFunctionOpt"
    /// );
    ///
    /// let qf_opt = QFunctionOpt::None;
    /// assert!(
    ///     !qf_opt.is_some_q_function_by_name(),
    ///     "Incorrect QFunctionOpt"
    /// );
    /// # Ok(())
    /// # }
    /// ```
    pub fn is_some_q_function_by_name(&self) -> bool {
        match self {
            Self::SomeQFunction(_) => false,
            Self::SomeQFunctionByName(_) => true,
            Self::None => false,
        }
    }

    /// Check if a QFunctionOpt is None
    ///
    /// ```
    /// # use libceed::prelude::*;
    /// # fn main() -> Result<(), libceed::CeedError> {
    /// # let ceed = libceed::Ceed::default_init();
    /// let mut user_f = |[u, weights, ..]: QFunctionInputs, [v, ..]: QFunctionOutputs| {
    ///     // Iterate over quadrature points
    ///     v.iter_mut()
    ///         .zip(u.iter().zip(weights.iter()))
    ///         .for_each(|(v, (u, w))| *v = u * w);
    ///
    ///     // Return clean error code
    ///     0
    /// };
    ///
    /// let qf = ceed
    ///     .q_function_interior(1, Box::new(user_f))?
    ///     .input("u", 1, EvalMode::Interp)?
    ///     .input("weights", 1, EvalMode::Weight)?
    ///     .output("v", 1, EvalMode::Interp)?;
    /// let qf_opt = QFunctionOpt::from(&qf);
    /// assert!(!qf_opt.is_none(), "Incorrect QFunctionOpt");
    ///
    /// let qf = ceed.q_function_interior_by_name("Mass1DBuild")?;
    /// let qf_opt = QFunctionOpt::from(&qf);
    /// assert!(!qf_opt.is_none(), "Incorrect QFunctionOpt");
    ///
    /// let qf_opt = QFunctionOpt::None;
    /// assert!(qf_opt.is_none(), "Incorrect QFunctionOpt");
    /// # Ok(())
    /// # }
    /// ```
    pub fn is_none(&self) -> bool {
        match self {
            Self::SomeQFunction(_) => false,
            Self::SomeQFunctionByName(_) => false,
            Self::None => true,
        }
    }
}

// -----------------------------------------------------------------------------
// CeedQFunction context wrapper
// -----------------------------------------------------------------------------
#[derive(Debug)]
pub(crate) struct QFunctionCore<'a> {
    ptr: bind_ceed::CeedQFunction,
    _lifeline: PhantomData<&'a ()>,
}

struct QFunctionTrampolineData {
    number_inputs: usize,
    number_outputs: usize,
    input_sizes: [usize; MAX_QFUNCTION_FIELDS],
    output_sizes: [usize; MAX_QFUNCTION_FIELDS],
    user_f: Box<QFunctionUserClosure>,
}

pub struct QFunction<'a> {
    qf_core: QFunctionCore<'a>,
    qf_ctx_ptr: bind_ceed::CeedQFunctionContext,
    trampoline_data: Pin<Box<QFunctionTrampolineData>>,
}

#[derive(Debug)]
pub struct QFunctionByName<'a> {
    qf_core: QFunctionCore<'a>,
}

// -----------------------------------------------------------------------------
// Destructor
// -----------------------------------------------------------------------------
impl<'a> Drop for QFunctionCore<'a> {
    fn drop(&mut self) {
        unsafe {
            if self.ptr != bind_ceed::CEED_QFUNCTION_NONE {
                bind_ceed::CeedQFunctionDestroy(&mut self.ptr);
            }
        }
    }
}

impl<'a> Drop for QFunction<'a> {
    fn drop(&mut self) {
        unsafe {
            bind_ceed::CeedQFunctionContextDestroy(&mut self.qf_ctx_ptr);
        }
    }
}

// -----------------------------------------------------------------------------
// Display
// -----------------------------------------------------------------------------
impl<'a> fmt::Display for QFunctionCore<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let mut ptr = std::ptr::null_mut();
        let mut sizeloc = crate::MAX_BUFFER_LENGTH;
        let cstring = unsafe {
            let file = bind_ceed::open_memstream(&mut ptr, &mut sizeloc);
            bind_ceed::CeedQFunctionView(self.ptr, file);
            bind_ceed::fclose(file);
            CString::from_raw(ptr)
        };
        cstring.to_string_lossy().fmt(f)
    }
}
/// View a QFunction
///
/// ```
/// # use libceed::prelude::*;
/// # fn main() -> Result<(), libceed::CeedError> {
/// # let ceed = libceed::Ceed::default_init();
/// let mut user_f = |[u, weights, ..]: QFunctionInputs, [v, ..]: QFunctionOutputs| {
///     // Iterate over quadrature points
///     v.iter_mut()
///         .zip(u.iter().zip(weights.iter()))
///         .for_each(|(v, (u, w))| *v = u * w);
///
///     // Return clean error code
///     0
/// };
///
/// let qf = ceed
///     .q_function_interior(1, Box::new(user_f))?
///     .input("u", 1, EvalMode::Interp)?
///     .input("weights", 1, EvalMode::Weight)?
///     .output("v", 1, EvalMode::Interp)?;
///
/// println!("{}", qf);
/// # Ok(())
/// # }
/// ```
impl<'a> fmt::Display for QFunction<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.qf_core.fmt(f)
    }
}

/// View a QFunction by Name
///
/// ```
/// # use libceed::prelude::*;
/// # fn main() -> Result<(), libceed::CeedError> {
/// # let ceed = libceed::Ceed::default_init();
/// let qf = ceed.q_function_interior_by_name("Mass1DBuild")?;
/// println!("{}", qf);
/// # Ok(())
/// # }
/// ```
impl<'a> fmt::Display for QFunctionByName<'a> {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.qf_core.fmt(f)
    }
}

// -----------------------------------------------------------------------------
// Core functionality
// -----------------------------------------------------------------------------
impl<'a> QFunctionCore<'a> {
    // Error handling
    #[doc(hidden)]
    fn check_error(&self, ierr: i32) -> crate::Result<i32> {
        let mut ptr = std::ptr::null_mut();
        unsafe {
            bind_ceed::CeedQFunctionGetCeed(self.ptr, &mut ptr);
        }
        crate::check_error(ptr, ierr)
    }

    // Common implementation
    pub fn apply(&self, Q: usize, u: &[Vector], v: &[Vector]) -> crate::Result<i32> {
        let mut u_c = [std::ptr::null_mut(); MAX_QFUNCTION_FIELDS];
        for i in 0..std::cmp::min(MAX_QFUNCTION_FIELDS, u.len()) {
            u_c[i] = u[i].ptr;
        }
        let mut v_c = [std::ptr::null_mut(); MAX_QFUNCTION_FIELDS];
        for i in 0..std::cmp::min(MAX_QFUNCTION_FIELDS, v.len()) {
            v_c[i] = v[i].ptr;
        }
        let Q = i32::try_from(Q).unwrap();
        let ierr = unsafe {
            bind_ceed::CeedQFunctionApply(self.ptr, Q, u_c.as_mut_ptr(), v_c.as_mut_ptr())
        };
        self.check_error(ierr)
    }
}

// -----------------------------------------------------------------------------
// User QFunction Closure
// -----------------------------------------------------------------------------
pub type QFunctionUserClosure = dyn FnMut(
    [&[crate::Scalar]; MAX_QFUNCTION_FIELDS],
    [&mut [crate::Scalar]; MAX_QFUNCTION_FIELDS],
) -> i32;

macro_rules! mut_max_fields {
    ($e:expr) => {
        [
            $e, $e, $e, $e, $e, $e, $e, $e, $e, $e, $e, $e, $e, $e, $e, $e,
        ]
    };
}
unsafe extern "C" fn trampoline(
    ctx: *mut ::std::os::raw::c_void,
    q: bind_ceed::CeedInt,
    inputs: *const *const bind_ceed::CeedScalar,
    outputs: *const *mut bind_ceed::CeedScalar,
) -> ::std::os::raw::c_int {
    let trampoline_data: Pin<&mut QFunctionTrampolineData> = std::mem::transmute(ctx);

    // Inputs
    let inputs_slice: &[*const bind_ceed::CeedScalar] =
        std::slice::from_raw_parts(inputs, MAX_QFUNCTION_FIELDS);
    let mut inputs_array: [&[crate::Scalar]; MAX_QFUNCTION_FIELDS] = [&[0.0]; MAX_QFUNCTION_FIELDS];
    inputs_slice
        .iter()
        .enumerate()
        .map(|(i, &x)| {
            std::slice::from_raw_parts(x, trampoline_data.input_sizes[i] * q as usize)
                as &[crate::Scalar]
        })
        .zip(inputs_array.iter_mut())
        .for_each(|(x, a)| *a = x);

    // Outputs
    let outputs_slice: &[*mut bind_ceed::CeedScalar] =
        std::slice::from_raw_parts(outputs, MAX_QFUNCTION_FIELDS);
    let mut outputs_array: [&mut [crate::Scalar]; MAX_QFUNCTION_FIELDS] =
        mut_max_fields!(&mut [0.0]);
    outputs_slice
        .iter()
        .enumerate()
        .map(|(i, &x)| {
            std::slice::from_raw_parts_mut(x, trampoline_data.output_sizes[i] * q as usize)
                as &mut [crate::Scalar]
        })
        .zip(outputs_array.iter_mut())
        .for_each(|(x, a)| *a = x);

    // User closure
    (trampoline_data.get_unchecked_mut().user_f)(inputs_array, outputs_array)
}

// -----------------------------------------------------------------------------
// QFunction
// -----------------------------------------------------------------------------
impl<'a> QFunction<'a> {
    // Constructor
    pub fn create(
        ceed: &'a crate::Ceed,
        vlength: usize,
        user_f: Box<QFunctionUserClosure>,
    ) -> crate::Result<Self> {
        let source_c = CString::new("").expect("CString::new failed");
        let mut ptr = std::ptr::null_mut();

        // Context for closure
        let number_inputs = 0;
        let number_outputs = 0;
        let input_sizes = [0; MAX_QFUNCTION_FIELDS];
        let output_sizes = [0; MAX_QFUNCTION_FIELDS];
        let trampoline_data = unsafe {
            Pin::new_unchecked(Box::new(QFunctionTrampolineData {
                number_inputs,
                number_outputs,
                input_sizes,
                output_sizes,
                user_f,
            }))
        };

        // Create QFunction
        let vlength = i32::try_from(vlength).unwrap();
        let mut ierr = unsafe {
            bind_ceed::CeedQFunctionCreateInterior(
                ceed.ptr,
                vlength,
                Some(trampoline),
                source_c.as_ptr(),
                &mut ptr,
            )
        };
        ceed.check_error(ierr)?;

        // Set closure
        let mut qf_ctx_ptr = std::ptr::null_mut();
        ierr = unsafe { bind_ceed::CeedQFunctionContextCreate(ceed.ptr, &mut qf_ctx_ptr) };
        ceed.check_error(ierr)?;
        ierr = unsafe {
            bind_ceed::CeedQFunctionContextSetData(
                qf_ctx_ptr,
                crate::MemType::Host as bind_ceed::CeedMemType,
                crate::CopyMode::UsePointer as bind_ceed::CeedCopyMode,
                std::mem::size_of::<QFunctionTrampolineData>() as u64,
                std::mem::transmute(trampoline_data.as_ref()),
            )
        };
        ceed.check_error(ierr)?;
        ierr = unsafe { bind_ceed::CeedQFunctionSetContext(ptr, qf_ctx_ptr) };
        ceed.check_error(ierr)?;
        Ok(Self {
            qf_core: QFunctionCore {
                ptr,
                _lifeline: PhantomData,
            },
            qf_ctx_ptr,
            trampoline_data,
        })
    }

    /// Apply the action of a QFunction
    ///
    /// * `Q`      - The number of quadrature points
    /// * `input`  - Array of input Vectors
    /// * `output` - Array of output Vectors
    ///
    /// ```
    /// # use libceed::prelude::*;
    /// # fn main() -> Result<(), libceed::CeedError> {
    /// # let ceed = libceed::Ceed::default_init();
    /// let mut user_f = |[u, weights, ..]: QFunctionInputs, [v, ..]: QFunctionOutputs| {
    ///     // Iterate over quadrature points
    ///     v.iter_mut()
    ///         .zip(u.iter().zip(weights.iter()))
    ///         .for_each(|(v, (u, w))| *v = u * w);
    ///
    ///     // Return clean error code
    ///     0
    /// };
    ///
    /// let qf = ceed
    ///     .q_function_interior(1, Box::new(user_f))?
    ///     .input("u", 1, EvalMode::Interp)?
    ///     .input("weights", 1, EvalMode::Weight)?
    ///     .output("v", 1, EvalMode::Interp)?;
    ///
    /// const Q: usize = 8;
    /// let mut w = [0.; Q];
    /// let mut u = [0.; Q];
    /// let mut v = [0.; Q];
    ///
    /// for i in 0..Q {
    ///     let x = 2. * (i as Scalar) / ((Q as Scalar) - 1.) - 1.;
    ///     u[i] = 2. + 3. * x + 5. * x * x;
    ///     w[i] = 1. - x * x;
    ///     v[i] = u[i] * w[i];
    /// }
    ///
    /// let uu = ceed.vector_from_slice(&u)?;
    /// let ww = ceed.vector_from_slice(&w)?;
    /// let mut vv = ceed.vector(Q)?;
    /// vv.set_value(0.0);
    /// {
    ///     let input = vec![uu, ww];
    ///     let mut output = vec![vv];
    ///     qf.apply(Q, &input, &output)?;
    ///     vv = output.remove(0);
    /// }
    ///
    /// vv.view()
    ///     .iter()
    ///     .zip(v.iter())
    ///     .for_each(|(computed, actual)| {
    ///         assert_eq!(
    ///             *computed, *actual,
    ///             "Incorrect value in QFunction application"
    ///         );
    ///     });
    /// # Ok(())
    /// # }
    /// ```
    pub fn apply(&self, Q: usize, u: &[Vector], v: &[Vector]) -> crate::Result<i32> {
        self.qf_core.apply(Q, u, v)
    }

    /// Add a QFunction input
    ///
    /// * `fieldname` - Name of QFunction field
    /// * `size`      - Size of QFunction field, `(ncomp * dim)` for `Grad` or
    ///                   `(ncomp * 1)` for `None`, `Interp`, and `Weight`
    /// * `emode`     - `EvalMode::None` to use values directly, `EvalMode::Interp`
    ///                   to use interpolated values, `EvalMode::Grad` to use
    ///                   gradients, `EvalMode::Weight` to use quadrature weights
    ///
    /// ```
    /// # use libceed::prelude::*;
    /// # fn main() -> Result<(), libceed::CeedError> {
    /// # let ceed = libceed::Ceed::default_init();
    /// let mut user_f = |[u, weights, ..]: QFunctionInputs, [v, ..]: QFunctionOutputs| {
    ///     // Iterate over quadrature points
    ///     v.iter_mut()
    ///         .zip(u.iter().zip(weights.iter()))
    ///         .for_each(|(v, (u, w))| *v = u * w);
    ///
    ///     // Return clean error code
    ///     0
    /// };
    ///
    /// let mut qf = ceed.q_function_interior(1, Box::new(user_f))?;
    ///
    /// qf = qf.input("u", 1, EvalMode::Interp)?;
    /// qf = qf.input("weights", 1, EvalMode::Weight)?;
    /// # Ok(())
    /// # }
    /// ```
    pub fn input(
        mut self,
        fieldname: &str,
        size: usize,
        emode: crate::EvalMode,
    ) -> crate::Result<Self> {
        let name_c = CString::new(fieldname).expect("CString::new failed");
        let idx = self.trampoline_data.number_inputs;
        self.trampoline_data.input_sizes[idx] = size;
        self.trampoline_data.number_inputs += 1;
        let (size, emode) = (
            i32::try_from(size).unwrap(),
            emode as bind_ceed::CeedEvalMode,
        );
        let ierr = unsafe {
            bind_ceed::CeedQFunctionAddInput(self.qf_core.ptr, name_c.as_ptr(), size, emode)
        };
        self.qf_core.check_error(ierr)?;
        Ok(self)
    }

    /// Add a QFunction output
    ///
    /// * `fieldname` - Name of QFunction field
    /// * `size`      - Size of QFunction field, `(ncomp * dim)` for `Grad` or
    ///                   `(ncomp * 1)` for `None` and `Interp`
    /// * `emode`     - `EvalMode::None` to use values directly, `EvalMode::Interp`
    ///                   to use interpolated values, `EvalMode::Grad` to use
    ///                   gradients
    ///
    /// ```
    /// # use libceed::prelude::*;
    /// # fn main() -> Result<(), libceed::CeedError> {
    /// # let ceed = libceed::Ceed::default_init();
    /// let mut user_f = |[u, weights, ..]: QFunctionInputs, [v, ..]: QFunctionOutputs| {
    ///     // Iterate over quadrature points
    ///     v.iter_mut()
    ///         .zip(u.iter().zip(weights.iter()))
    ///         .for_each(|(v, (u, w))| *v = u * w);
    ///
    ///     // Return clean error code
    ///     0
    /// };
    ///
    /// let mut qf = ceed.q_function_interior(1, Box::new(user_f))?;
    ///
    /// qf.output("v", 1, EvalMode::Interp)?;
    /// # Ok(())
    /// # }
    /// ```
    pub fn output(
        mut self,
        fieldname: &str,
        size: usize,
        emode: crate::EvalMode,
    ) -> crate::Result<Self> {
        let name_c = CString::new(fieldname).expect("CString::new failed");
        let idx = self.trampoline_data.number_outputs;
        self.trampoline_data.output_sizes[idx] = size;
        self.trampoline_data.number_outputs += 1;
        let (size, emode) = (
            i32::try_from(size).unwrap(),
            emode as bind_ceed::CeedEvalMode,
        );
        let ierr = unsafe {
            bind_ceed::CeedQFunctionAddOutput(self.qf_core.ptr, name_c.as_ptr(), size, emode)
        };
        self.qf_core.check_error(ierr)?;
        Ok(self)
    }
}

// -----------------------------------------------------------------------------
// QFunction
// -----------------------------------------------------------------------------
impl<'a> QFunctionByName<'a> {
    // Constructor
    pub fn create(ceed: &'a crate::Ceed, name: &str) -> crate::Result<Self> {
        let name_c = CString::new(name).expect("CString::new failed");
        let mut ptr = std::ptr::null_mut();
        let ierr = unsafe {
            bind_ceed::CeedQFunctionCreateInteriorByName(ceed.ptr, name_c.as_ptr(), &mut ptr)
        };
        ceed.check_error(ierr)?;
        Ok(Self {
            qf_core: QFunctionCore {
                ptr,
                _lifeline: PhantomData,
            },
        })
    }

    /// Apply the action of a QFunction
    ///
    /// * `Q`      - The number of quadrature points
    /// * `input`  - Array of input Vectors
    /// * `output` - Array of output Vectors
    ///
    /// ```
    /// # use libceed::prelude::*;
    /// # fn main() -> Result<(), libceed::CeedError> {
    /// # let ceed = libceed::Ceed::default_init();
    /// const Q: usize = 8;
    /// let qf_build = ceed.q_function_interior_by_name("Mass1DBuild")?;
    /// let qf_mass = ceed.q_function_interior_by_name("MassApply")?;
    ///
    /// let mut j = [0.; Q];
    /// let mut w = [0.; Q];
    /// let mut u = [0.; Q];
    /// let mut v = [0.; Q];
    ///
    /// for i in 0..Q {
    ///     let x = 2. * (i as Scalar) / ((Q as Scalar) - 1.) - 1.;
    ///     j[i] = 1.;
    ///     w[i] = 1. - x * x;
    ///     u[i] = 2. + 3. * x + 5. * x * x;
    ///     v[i] = w[i] * u[i];
    /// }
    ///
    /// let jj = ceed.vector_from_slice(&j)?;
    /// let ww = ceed.vector_from_slice(&w)?;
    /// let uu = ceed.vector_from_slice(&u)?;
    /// let mut vv = ceed.vector(Q)?;
    /// vv.set_value(0.0);
    /// let mut qdata = ceed.vector(Q)?;
    /// qdata.set_value(0.0);
    ///
    /// {
    ///     let mut input = vec![jj, ww];
    ///     let mut output = vec![qdata];
    ///     qf_build.apply(Q, &input, &output)?;
    ///     qdata = output.remove(0);
    /// }
    ///
    /// {
    ///     let mut input = vec![qdata, uu];
    ///     let mut output = vec![vv];
    ///     qf_mass.apply(Q, &input, &output)?;
    ///     vv = output.remove(0);
    /// }
    ///
    /// vv.view()
    ///     .iter()
    ///     .zip(v.iter())
    ///     .for_each(|(computed, actual)| {
    ///         assert_eq!(
    ///             *computed, *actual,
    ///             "Incorrect value in QFunction application"
    ///         );
    ///     });
    /// # Ok(())
    /// # }
    /// ```
    pub fn apply(&self, Q: usize, u: &[Vector], v: &[Vector]) -> crate::Result<i32> {
        self.qf_core.apply(Q, u, v)
    }
}

// -----------------------------------------------------------------------------