Revert documentation comments

fem/coefficient.hpp

@@ -1056,24 +1056,7 @@ public:
 typedef VectorCoefficient DiagonalMatrixCoefficient;
 
 /** Base class for matrix-valued coefficients that optionally depend on time
-    and space.
-
-    A `MatrixCoefficient` represents a linear map from a vector of length
-    `width` to a vector of length `height`. The matrix entries returned by
-    `Eval()` follow the usual row/column convention:
-
-       y(i) = sum_j K(i,j) x(j)
-
-    so row `i` corresponds to output component `i` and column `j` corresponds
-    to input component `j`.
-
-    In bilinear forms this means that, for a matrix coefficient `M`, MFEM uses
-    the evaluated matrix in the natural way, e.g. `test . (M trial)`. For mixed
-    forms, `height` should therefore match the vector dimension of the test
-    space and `width` should match the vector dimension of the trial space.
-
-    Example: to represent the 3D cross product `v x u`, `Eval()` should fill
-    `K` so that `K * u` equals `v x u`. */
+    and space. */
 class MatrixCoefficient
 {
 protected:
@@ -1109,9 +1092,7 @@ public:
    bool IsSymmetric() const { return symmetric; }
 
    /** @brief Evaluate the matrix coefficient in the element described by @a T
-       at the point @a ip, storing the result in @a K.
-       @note The returned matrix should satisfy `y = K x` with entries
-       `y(i) = sum_j K(i,j) x(j)`. */
+       at the point @a ip, storing the result in @a K. */
    /** @note When this method is called, the caller must make sure that the
        IntegrationPoint associated with @a T is the same as @a ip. This can be
        achieved by calling T.SetIntPoint(&ip). */