Spatial phase distribution is oppositely observed for imagesc and pcolor plots

clc;

[x,y] = meshgrid(linspace(-0.6, 0.6), linspace(-0.6, 0.6));

[phi,r] = cart2pol(x,y);

% Omega_r -vortex beam specification

l = 2;

p = 2;

w0 = 0.2;

R = sqrt(2).*r./w0;

RR = r./w0;

Omega01 = exp(-RR.^2);

Lpl = 0;

for m = 0:p;

Lpl = Lpl + (((-1).^m)./factorial(m)).*nchoosek(p+l,p-m).*(R.^(2.*m));

end;

Omega_r = Omega01.*(RR.^(abs(l))).*Lpl.*exp(-i.*l.*phi);

%figure;

%imagesc(angle(Omega_r));

%colormap jet

%colorbar

pcolor(x, y, angle(Omega_r))

shading interp

colormap jet

colorbar

Answer 1

[Vinayak]

Hi Pradipta,

The reason the two plots appear as flipped images of each other on the y-axis is due to the different default y-axis directions of 'imagesc' and 'pcolor'. For 'imagesc', the (1,1) element of the matrix is placed at the bottom-left corner of the axes by default, whereas for 'pcolor', it's placed at the top-left corner.

To make the plots similar, we can reverse the y-axis for 'imagesc' as follows:

[x, y] = meshgrid(linspace(-0.6, 0.6), linspace(-0.6, 0.6));
[phi, r] = cart2pol(x, y);

% Omega_r - vortex beam specification
l = 2;
p = 2;
w0 = 0.2;
R = sqrt(2) .* r ./ w0;
RR = r ./ w0;
Omega01 = exp(-RR.^2);
Lpl = 0;
for m = 0:p
    Lpl = Lpl + (((-1).^m) ./ factorial(m)) .* nchoosek(p+l, p-m) .* (R .^ (2.*m));
end
Omega_r = Omega01 .* (RR .^ (abs(l))) .* Lpl .* exp(-1i .* l .* phi);

% Using imagesc
figure;
imagesc(x(1,:), y(:,1), angle(Omega_r)); % Ensure axes are consistent
axis xy; % Reverse y-axis direction to match pcolor
colormap jet;
colorbar;
title('imagesc');

% Using pcolor
figure;
pcolor(x, y, angle(Omega_r));
shading interp;
colormap jet;
colorbar;
title('pcolor');

[Pradipta Panchadhyayee]

Than yoy your useful response. Again thank you.