diff --git a/src/permanents.h b/src/permanents.h
new file mode 100644
index 0000000..153ce14
--- /dev/null
+++ b/src/permanents.h
@@ -0,0 +1,22 @@
+// Ryser's algorithm 
+static npy_complex128 perm_ryser(PyArrayObject *submatrix) {
+    int n = (int) PyArray_DIM(submatrix, 0);
+    npy_complex128 rowsum, rowsumprod;
+    npy_complex128 perm = complex_zero;
+    int exp = 1 << n; 
+    int i, y, z;
+    for (i=0; i<exp; ++i) {
+        rowsumprod = complex_one;
+        for (y=0; y<n; ++y) {               
+            rowsum = complex_zero;
+            for (z=0; z<n; ++z) { 
+                if ((i & (1 << z)) != 0) { complex_inc(&rowsum, SM(z, y)); }
+            }
+            complex_multiply(&rowsumprod, rowsum);
+        }
+        complex_inc(&perm, complex_float_prod(rowsumprod, bitparity(i)));
+    }
+    if (n%2 == 1) {perm=complex_float_prod(perm, -1);}
+    return perm;
+}
+