a slightly different matrix product

test/monniaux/many_temporaries/matrix_product2.py

+m=4
+n=5
+p=6
+number_type='double'
+with open('matrix_product2.c', 'w') as cfile:
+    cfile.write(f'void matrix_product({number_type} c[{m}][{p}], const {number_type} a[{m}][{n}], const {number_type} b[{n}][{p}]) {{\n')
+    for i in range(m):
+        for j in range(n):
+            for k in range(p):
+                cfile.write(f'  const {number_type} p_{i}_{j}_{k} = a[{i}][{j}] * b[{j}][{k}];\n')
+    for i in range(m):
+        for k in range(p):
+            cfile.write(f'  const {number_type} r_{i}_{k} = ')
+            for j in range(n):
+                if j>0:
+                    cfile.write(' + ')
+                cfile.write(f'p_{i}_{j}_{k}')
+            cfile.write(';\n')
+    for i in range(m):
+        for k in range(p):
+            cfile.write(f'  c[{i}][{k}] = r_{i}_{k};\n')
+    
+    cfile.write('}\n')
+