Matrix multiplication: Difference between revisions

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 =={{header|C}}==
 {{works with|gcc|<nowiki>4.1.2 20070925 (Red Hat 4.1.2-27) Options: gcc -std=gnu99</nowiki>}}
+<c>
- #include <stdio.h>
+#include <stdio.h>
- #define dim 4 /* fixed length square matrices */
+#define dim 4 /* fixed length square matrices */
- const int SLICE=0; /* coder hints */
+const int SLICE=0; /* coder hints */
- typedef double field_t; /* field_t type is long float */
+typedef double field_t; /* field_t type is long float */
- typedef field_t vec_t[dim];
- typedef field_t *ref_vec_t; /* address of first element */
+typedef field_t vec_t[dim];
+typedef field_t *ref_vec_t; /* address of first element */
- typedef vec_t matrix_t[dim];
+typedef vec_t matrix_t[dim];
- typedef field_t *ref_matrix_t; /* address of first element */
+typedef field_t *ref_matrix_t; /* address of first element */
- typedef char* format;
+typedef char* format;
+/* define the vector/matrix_t operators */
+field_t v_times_v (vec_t a, vec_t b, int step_b){
+    /* basically the dot product if step_b==1*/
+    field_t result=0;
+    for( int i=0; i<sizeof a; i++ )
+      result+= a[i]*b[i*step_b];
+    return result;
+  }
+ref_vec_t v_eq_v_times_m(vec_t result, vec_t a, matrix_t b){
+    for( int j=0; j<sizeof b; j++ )
+      result[j]=v_times_v(a,&b[SLICE][j],sizeof b[SLICE] / sizeof (field_t));
+    return &result[SLICE];
+  }
+ref_matrix_t m_eq_m_times_m (matrix_t result, matrix_t a, matrix_t b){
+    for( int k=0; k<sizeof result; k++ )
+      v_eq_v_times_m(&result[k][SLICE],&a[k][SLICE],b);
+    return &result[SLICE][SLICE];
+  }
+/* Some sample matrices to test */
+matrix_t a={{1,  1,  1,   1}, /* matrix_t A */
+            {2,  4,  8,  16},
+            {3,  9, 27,  81},
+            {4, 16, 64, 256}};
+matrix_t b={{  4.0  , -3.0  ,  4.0/3,  -1.0/4 }, /* matrix_t B */
+            {-13.0/3, 19.0/4, -7.0/3,  11.0/24},
+            {  3.0/2, -2.0  ,  7.0/6,  -1.0/4 },
+            { -1.0/6,  1.0/4, -1.0/6,   1.0/24}};
+int main(){
+  matrix_t prod;
+  m_eq_m_times_m(prod,a,b); /* actual multiplication example of A x B */
+  #define field_fmt "%6.2f" /* width of 6, with no '+' sign, 2 decimals */
+  #define vec_fmt "{"field_fmt","field_fmt","field_fmt","field_fmt"}"
+  #define matrix_fmt " {"vec_fmt",\n  "vec_fmt",\n  "vec_fmt",\n  "vec_fmt"};"
+  format result_fmt = " Product of a and b: \n"matrix_fmt"\n";
- /* define the vector/matrix_t operators */
+  /* finally print the result */
- field_t v_times_v (vec_t a, vec_t b, int step_b){
+  vprintf(result_fmt,(void*)&prod);
-     /* basically the dot product if step_b==1*/
+}
-     field_t result=0;
+</c>
-     for( int i=0; i<sizeof a; i++ )
-       result+= a[i]*b[i*step_b];
-     return result;
-   }
- ref_vec_t v_eq_v_times_m(vec_t result, vec_t a, matrix_t b){
-     for( int j=0; j<sizeof b; j++ )
-       result[j]=v_times_v(a,&b[SLICE][j],sizeof b[SLICE] / sizeof (field_t));
-     return &result[SLICE];
-   }
- ref_matrix_t m_eq_m_times_m (matrix_t result, matrix_t a, matrix_t b){
-     for( int k=0; k<sizeof result; k++ )
-       v_eq_v_times_m(&result[k][SLICE],&a[k][SLICE],b);
-     return &result[SLICE][SLICE];
-   }
- /* Some sample matrices to test */
- matrix_t a={{1,  1,  1,   1}, /* matrix_t A */
-             {2,  4,  8,  16},
-             {3,  9, 27,  81},
-             {4, 16, 64, 256}};
- matrix_t b={{  4.0  , -3.0  ,  4.0/3,  -1.0/4 }, /* matrix_t B */
-             {-13.0/3, 19.0/4, -7.0/3,  11.0/24},
-             {  3.0/2, -2.0  ,  7.0/6,  -1.0/4 },
-             { -1.0/6,  1.0/4, -1.0/6,   1.0/24}};
- int main(){
-   matrix_t prod;
-   m_eq_m_times_m(prod,a,b); /* actual multiplication example of A x B */
-   #define field_fmt "%6.2f" /* width of 6, with no '+' sign, 2 decimals */
-   #define vec_fmt "{"field_fmt","field_fmt","field_fmt","field_fmt"}"
-   #define matrix_fmt " {"vec_fmt",\n  "vec_fmt",\n  "vec_fmt",\n  "vec_fmt"};"
-   format result_fmt = " Product of a and b: \n"matrix_fmt"\n";
-   /* finally print the result */
-   vprintf(result_fmt,(void*)&prod);
- }
 Output:
  Product of a and b: