1 files changed, 20 insertions, 0 deletions
diff --git a/src/misc.c b/src/misc.c
index ba0a090..d20bc26 100644
--- a/src/misc.c
+++ b/src/misc.c
@@ -218,6 +218,26 @@ static struct {
     {100,363.73937555556347},
 };
 
+double trapz(const double *y, double dx, size_t n)
+{
+    /* Returns the integral of `y` using the trapezoidal rule assuming a
+     * constant grid spacing `dx`.
+     *
+     * See https://en.wikipedia.org/wiki/Trapezoidal_rule. */
+    size_t i;
+    double sum = 0.0;
+
+    if (n < 2) return 0.0;
+
+    sum = y[0];
+    for (i = 1; i < n-1; i++) {
+        sum += 2*y[i];
+    }
+    sum += y[n-1];
+
+    return sum*dx/2.0;
+}
+
 void get_path_length(double *pos1, double *pos2, double R, double *l1, double *l2)
 {
     /* Returns the path length inside and outside a circle of radius `R` for a