From d0bdb50f24280aea97777a03c2a390a6913e5771 Mon Sep 17 00:00:00 2001
From: Peter Boyle <paboyle@ph.ed.ac.uk>
Date: Tue, 27 Aug 2024 10:58:19 -0400
Subject: [PATCH] Analyse power spectrum

---
 Grid/algorithms/iterative/PowerSpectrum.h | 76 +++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 Grid/algorithms/iterative/PowerSpectrum.h

diff --git a/Grid/algorithms/iterative/PowerSpectrum.h b/Grid/algorithms/iterative/PowerSpectrum.h
new file mode 100644
index 00000000..353a5770
--- /dev/null
+++ b/Grid/algorithms/iterative/PowerSpectrum.h
@@ -0,0 +1,76 @@
+#pragma once
+namespace Grid {
+
+class Band
+{
+  RealD lo, hi;
+public:
+  Band(RealD _lo,RealD _hi)
+  {
+    lo=_lo;
+    hi=_hi;
+  }
+  RealD operator() (RealD x){
+    if ( x>lo && x<hi ){
+      return 1.0;
+    } else {
+      return 0.0;
+    }
+  }
+};
+
+class PowerSpectrum
+{ 
+ public: 
+
+  template<typename T>  static RealD normalise(T& v) 
+  {
+    RealD nn = norm2(v);
+    nn = sqrt(nn);
+    v = v * (1.0/nn);
+    return nn;
+  }
+
+  std::vector<RealD> ranges;
+  std::vector<int> order;
+  
+  PowerSpectrum(  std::vector<RealD> &bins, std::vector<int> &_order ) : ranges(bins), order(_order)  { };
+
+  template<class Field>
+  RealD operator()(LinearOperatorBase<Field> &HermOp, const Field &src) 
+  { 
+    GridBase *grid = src.Grid(); 
+    int N=ranges.size();
+    RealD hi = ranges[N-1];
+
+    RealD lo_band = 0.0;
+    RealD hi_band;
+    RealD nn=norm2(src);
+    RealD ss=0.0;
+
+    Field tmp = src;
+
+    for(int b=0;b<N;b++){
+      hi_band = ranges[b];
+      Band Notch(lo_band,hi_band);
+      
+      Chebyshev<Field> polynomial;
+      polynomial.Init(0.0,hi,order[b],Notch);
+      polynomial.JacksonSmooth();
+
+      polynomial(HermOp,src,tmp) ;
+
+      RealD p=norm2(tmp);
+      ss=ss+p;
+      std::cout << GridLogMessage << " PowerSpectrum Band["<<lo_band<<","<<hi_band<<"] power "<<norm2(tmp)/nn<<std::endl;
+      
+      lo_band=hi_band;
+    }
+    std::cout << GridLogMessage << " PowerSpectrum total power "<<ss/nn<<std::endl;
+    std::cout << GridLogMessage << " PowerSpectrum total power (unnormalised) "<<nn<<std::endl;
+
+    return 0;
+  };
+};
+  
+}