Canny Edge Detection, non-maximum suppression

I am trying to implant Canny Edge Detection algorithm.

I started first with decomposing it using matlab functions.

function [newImg, tgTeta] = edgeDetectMatlab(img)
  newImg=zeros(size(img));
  tgTeta=zeros(size(img));
  
  smoothImg=imgaussfilt(img,1.4);
  [fx,fy]=imgradientxy(img);
  tgTeta=imgradient(img);
end

I know that 2 steps are missing: non-maximum suppression and double threshold, but how can I do an non-maximum suppression?

[Image Analyst]

There is a Canny method in the edge() function. Why not use that?