1 files changed, 63 insertions, 0 deletions
diff --git a/lib/sigmoid.c b/lib/sigmoid.c
new file mode 100644
index 0000000..05ea126
--- /dev/null
+++ b/lib/sigmoid.c
@@ -0,0 +1,63 @@
+// Sigmoid
+//
+// sigmoid - sig
+//
+// f(x) = ( L / ( 1 + e^( -( 4m * ( x - x_0 ) / L ) ) ) ) + b - ( L / 2 )
+//
+// m = f'(0)
+// b = f(0)
+// ( b - ( L / 2 ) ) < y < ( b + ( L / 2 ) )
+//
+// X_n - 1
+// Y_n - 1
+// C_n - 3
+//
+// c[0] = m
+// c[1] = L
+// c[2] = b
+
+
+#include <math.h>
+#include "ts.h"
+
+
+typedef struct {
+    fp_t m;
+    fp_t L;
+    fp_t b;
+} ts_sigmoid_params_t;
+
+ts_parameter_t const ts_sigmoid_p = { .n_inputs = 1, .n_outputs = 1, .n_constants = 3, .params_size = sizeof(ts_sigmoid_params_t) };
+
+
+uint_t ts_sigmoid_offset( ts_constant_t const *c )
+{
+	( void )c;
+	return ( 0 );
+}
+
+int ts_sigmoid(
+	fp_t * const *y, uint_t y_n,
+	fp_t const * const *x, uint_t x_n,
+	uint_t n, ts_constant_t const *c
+)
+{
+	TS_PROLOGUE( ts_sigmoid_p );
+	if ( !c ) return -1;
+	fp_t m = ((ts_sigmoid_params_t *)c)->m;
+	fp_t L = ((ts_sigmoid_params_t *)c)->L;
+	fp_t b = ((ts_sigmoid_params_t *)c)->b;
+
+	m = -( 4.0 * m ) / L;
+    b = b - ( 0.5 * L );
+
+	for( uint_t i = 0; i < n; ++i )
+	{
+		fp_t xv = m * x[0][i];
+		if( xv > 500.0 ) { y[0][i] = b; continue; }
+		if( xv < -500.0 ) { y[0][i] = L + b; continue; }
+		y[0][i] = ( L / ( 1.0 + exp( xv ) ) ) + b;
+	}
+	return 0;
+}
+