From cbe8a1cecc84315aeb22fa5d4d8fc3c93b053407 Mon Sep 17 00:00:00 2001
From: Seb James <sebj_coder3@pm.me>
Date: Wed, 23 Sep 2026 10:10:35 +0100
Subject: [PATCH] Adds function to conveniently obtain the real part of the
 inverse.

---
 sm/hexfft.cppm    | 11 +++++++++++
 tests/hexfft1.cpp |  4 ++++
 2 files changed, 15 insertions(+)

diff --git a/sm/hexfft.cppm b/sm/hexfft.cppm
index d7c6b47..b8d6d04 100644
--- a/sm/hexfft.cppm
+++ b/sm/hexfft.cppm
@@ -408,6 +408,17 @@ export namespace sm::hexfft
             return this->image_asa_to_hexgrid();
         }
 
+        //! Return the real component of the inverse FFT.
+        sm::vvec<F> inverse_real()
+        {
+            sm::vvec<std::complex<F>> inv_cplx = this->inverse();
+            sm::vvec<F> inv_real (inv_cplx.size(), F{0});
+            for (std::uint32_t i = 0; i < inv_cplx.size(); ++i) {
+                inv_real[i] = std::real (inv_cplx[i]);
+            }
+            return inv_real;
+        }
+
     private:
 
         //! Find parameters for the enclosing hexgrid (used to populate d0/d1 and create hg_asa)
diff --git a/tests/hexfft1.cpp b/tests/hexfft1.cpp
index d6698f8..159201d 100644
--- a/tests/hexfft1.cpp
+++ b/tests/hexfft1.cpp
@@ -27,10 +27,14 @@ static bool roundtrips (sm::hexgrid<F>& hg, const char* label)
     sm::hexfft::fft<F> hfft (&hg, data);
     sm::vvec<std::complex<F>> back = hfft.inverse();
 
+    sm::vvec<F> back_real = hfft.inverse_real();
+
     F maxerr = F{0};
     for (std::uint32_t i = 0; i < hg.num(); ++i) {
         F err = std::abs (back[i] - std::complex<F> (data[i], F{0}));
+        F err_real = std::abs (back_real[i] - data[i]);
         maxerr = std::max (maxerr, err);
+        maxerr = std::max (maxerr, err_real);
     }
     std::cout << label << ": hg.num()=" << hg.num() << " spectrum rows=" << hfft.asa_rows << " cols=" << hfft.asa_cols
                << " (size " << hfft.size() << ") max roundtrip error: " << maxerr << std::endl;