From 13ede1df912c7adc59535036103a2da640613bfe Mon Sep 17 00:00:00 2001
From: Luke Hutton <luke.hutton@arm.com>
Date: Mon, 9 Jan 2023 10:41:33 +0000
Subject: RFFT2D: Adjust output height to be same as the input

The expected output shape of RFFT2d should be (N, H, W/2+1) as
opposed to (N, H/2+1, W/2+1).

Change-Id: I66d830f1ffa86417b57572b3cd904db0290cac42
---
 chapters/tensor_ops.adoc | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

(limited to 'chapters/tensor_ops.adoc')

diff --git a/chapters/tensor_ops.adoc b/chapters/tensor_ops.adoc
index b8527bf..cb268fa 100644
--- a/chapters/tensor_ops.adoc
+++ b/chapters/tensor_ops.adoc
@@ -338,10 +338,12 @@ for_each(0 <= n < N, 0 <= oy < H, 0 <= ox < W, 0 <= c < C ) {
 
 Performs a batched 2D real-valued Fast Fourier Transform over the input where the input tensor consists of real values producing complex valued output.
 The complex output values will be split into the output_real and output_imag tensor arguments.
-RFFT2D takes advantage of Hermitian symmetry to only calculate the first half of the output.
-Imaginary values with locations h=0,H/2 or w=0,W/2 are zero.
+RFFT2D takes advantage of Hermitian symmetry to only calculate the first half of the final output axis.
+Imaginary values with locations (0,0), (0,W/2), (H/2,0) and (H/2,W/2) are zero.
 
-image::forward_fft2d.svg["forward FFT definition", align="center"]
+// output[h][w] = \sum_{m=0}^{H-1}\sum_{n=0}^{W-1}input[m][n] * \exp\left(-2\pi i\left(\frac{mh}{H} + \frac{nw}{W}\right)\right)
+
+image::forward_fft2d.svg["forward RFFT definition", align="center"]
 
 include::{generated}/operators/RFFT2D.adoc[]
 
@@ -350,7 +352,7 @@ include::{generated}/operators/RFFT2D.adoc[]
 ERROR_IF(!power_of_two(H));
 ERROR_IF(!power_of_two(W));
 
-for_each(0 <= n < N, 0 <= oy < H/2 + 1, 0 <= ox < W/2 + 1) {
+for_each(0 <= n < N, 0 <= oy < H, 0 <= ox < W/2 + 1) {
     in_out_t sum_real = 0.0;
     in_out_t sum_imag = 0.0;
     for_each(0 <= iy < H, 0 <= ix < W) {
-- 
cgit v1.2.1

