From 81979f09cf100db32deb0e1917dabb1fe435194c Mon Sep 17 00:00:00 2001
From: Elizabeth Hunt <elizabeth.hunt@simponic.xyz>
Date: Mon, 23 Oct 2023 10:17:03 -0600
Subject: [PATCH] matrix multiplication!

---
 inc/lizfcm.h    |  2 ++
 src/matrix.c    | 27 +++++++++++++++++++++++++++
 test/matrix.t.c | 36 ++++++++++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+)

diff --git a/inc/lizfcm.h b/inc/lizfcm.h
index b59651e..12c1278 100644
--- a/inc/lizfcm.h
+++ b/inc/lizfcm.h
@@ -35,6 +35,8 @@ extern Array_double *bsubst(Matrix_double *u, Array_double *b);
 extern Array_double *fsubst(Matrix_double *l, Array_double *b);
 extern Array_double *solve_matrix(Matrix_double *m, Array_double *b);
 extern Array_double *m_dot_v(Matrix_double *m, Array_double *v);
+extern Matrix_double *m_dot_m(Matrix_double *a, Matrix_double *b);
+extern Array_double *col_v(Matrix_double *m, size_t x);
 extern Matrix_double *copy_matrix(Matrix_double *m);
 extern void free_matrix(Matrix_double *m);
 extern void format_matrix_into(Matrix_double *m, char *s);
diff --git a/src/matrix.c b/src/matrix.c
index 5766d94..22dd171 100644
--- a/src/matrix.c
+++ b/src/matrix.c
@@ -14,6 +14,33 @@ Array_double *m_dot_v(Matrix_double *m, Array_double *v) {
   return product;
 }
 
+Array_double *col_v(Matrix_double *m, size_t x) {
+  assert(x < m->cols);
+
+  Array_double *col = InitArrayWithSize(double, m->rows, 0.0);
+  for (size_t y = 0; y < m->rows; y++)
+    col->data[y] = m->data[y]->data[x];
+
+  return col;
+}
+
+Matrix_double *m_dot_m(Matrix_double *a, Matrix_double *b) {
+  assert(a->cols == b->rows);
+
+  Matrix_double *prod = InitMatrixWithSize(double, a->rows, b->cols, 0.0);
+
+  Array_double *curr_col;
+  for (size_t y = 0; y < a->rows; y++) {
+    for (size_t x = 0; x < b->cols; x++) {
+      curr_col = col_v(b, x);
+      prod->data[y]->data[x] = v_dot_v(curr_col, a->data[y]);
+      free_vector(curr_col);
+    }
+  }
+
+  return prod;
+}
+
 Matrix_double *put_identity_diagonal(Matrix_double *m) {
   assert(m->rows == m->cols);
   Matrix_double *copy = copy_matrix(m);
diff --git a/test/matrix.t.c b/test/matrix.t.c
index 1def9ef..5386635 100644
--- a/test/matrix.t.c
+++ b/test/matrix.t.c
@@ -94,3 +94,39 @@ UTEST(matrix, solve_matrix) {
   free_vector(b);
   free_vector(solution);
 }
+
+UTEST(matrix, col_v) {
+  Matrix_double *m = InitMatrixWithSize(double, 2, 3, 0.0);
+  // set element to its column index
+  for (size_t y = 0; y < m->rows; y++) {
+    for (size_t x = 0; x < m->cols; x++) {
+      m->data[y]->data[x] = x;
+    }
+  }
+
+  Array_double *col, *expected;
+  for (size_t x = 0; x < m->cols; x++) {
+    col = col_v(m, x);
+    expected = InitArrayWithSize(double, m->rows, (double)x);
+    EXPECT_TRUE(vector_equal(expected, col));
+    free_vector(col);
+    free_vector(expected);
+  }
+
+  free_matrix(m);
+}
+
+UTEST(matrix, m_dot_m) {
+  Matrix_double *a = InitMatrixWithSize(double, 1, 3, 12.0);
+  Matrix_double *b = InitMatrixWithSize(double, 3, 1, 10.0);
+
+  Matrix_double *prod = m_dot_m(a, b);
+
+  EXPECT_EQ(prod->cols, 1);
+  EXPECT_EQ(prod->rows, 1);
+  EXPECT_EQ(12.0 * 10.0 * 3, prod->data[0]->data[0]);
+
+  free_matrix(a);
+  free_matrix(b);
+  free_matrix(prod);
+}