efficient computation of the smallest fourier mode by doing a magnetization-style update anytime a bond with the external field changes

1 files changed, 6 insertions, 8 deletions

diff --git a/lib/correlation.h b/lib/correlation.h
index b3b7d86..26c3a99 100644
--- a/lib/correlation.h
+++ b/lib/correlation.h
@@ -7,15 +7,13 @@
 #include <fftw3.h>
 
 template <class R_t, class X_t>
-double correlation_length(const state_t <R_t, X_t> *s, fftw_plan plan, double *in, double *out) {
-  for (v_t i = 0; i < s->nv; i++) {
-    in[i] = correlation_component(s->spins[i]);
-  }
-
-  fftw_execute(plan);
+double correlation_length(const state_t <R_t, X_t> *s) {
+  double total = 0;
 
-  double length = pow(out[0], 2);
+  for (D_t j = 0; j < s->D; j++) {
+    total += norm_squared(s->ReF[j]) + norm_squared(s->ImF[j]);
+  }
 
-  return length;
+  return total / s->D;
 }