- A reasonably-safe set of simplifications, much better than
- simplify() and safer than simplify_full()
+ Symbolic matrices have a `subs()` method, but no `subs_expr()`.
+ This makes it diffucult to substitute in a list of solutions obtained
+ with `solve()`.
+
+ INPUT:
+
+ - ``m`` -- A symbolic matrix.
+
+ - ``equations`` - One or more symbolic equations, presumably for
+ the entries of `m`.
+
+ OUTPUT:
+
+ The result of substituting each equation into `m`, one after another.
+
+ EXAMPLES::
+
+ sage: w,x,y,z = SR.var('w,x,y,z')
+ sage: A = matrix(SR, [[w,x],[y,z]])
+ sage: matrix_subs_expr(A, w == 1, x == 2, y == 3, z == 4)
+ [1 2]
+ [3 4]