[math] Adding sigmoid and softmax functions

src/logistic.c

@@ -0,0 +1,36 @@
+#include "logistic.h"
+#include "vector_math.h"
+
+inline double sigmoid(double x) {
+    return 1.0/(1.0 + exp(-x));
+}
+
+inline void sigmoid_vector(double *x, size_t n) {
+    for (int i = 0; i < n; i++) {
+        x[i] = sigmoid(x[i]);
+    }
+}
+
+inline void softmax_vector(double *x, size_t n) {
+    int i;
+    double sum = 0.0;
+    
+    double denom = double_array_log_sum_exp(x, n);
+
+    for (i = 0; i < n; i++) {
+        x[i] = exp(x[i] - denom);
+    }
+}
+
+
+void softmax_matrix(matrix_t *matrix) {
+    size_t num_rows = matrix->m;
+    size_t num_cols = matrix->n;
+
+    double *values = matrix->values;
+
+    for (int i = 0; i < num_rows; i++) {
+        softmax_vector(values, num_cols);
+        values += num_cols;
+    }
+}

src/logistic.h

@@ -0,0 +1,14 @@
+#ifndef LOGISTIC_H
+#define LOGISTIC_H
+
+#include <stdlib.h>
+#include <stdint.h>
+
+#include "matrix.h"
+
+double sigmoid(double x);
+void sigmoid_vector(double *x, size_t n);
+void softmax_vector(double *x, size_t n);
+void softmax_matrix(matrix_t *matrix);
+
+#endif