2d scan plot in matlab

Hi,

I want to scan over 2 quantities lets say x and y. For every value of x, I scan over a range of y and record value z for every point. So I have an (x,y) grid and have z which is an x by y matrix. How would I do a 2D plot of over such quantities. Many thanks for any lead.

Answer 1

[Star Strider]

What your Question lacks in clarity it makes up for in obfuscation.

See if my Answer to Create array from table with observations with two codes will do what you want.

[Sumera Yamin]

Many thanks for your reply. i do not want to creat an array, my problem is with plotting. Lets say i already have an array how would i plot a quantity z (which is a x by y matrix) over an (x,y) grid. How would i plot this data.

[Star Strider]

Using that code, try this:

figure
imagesc(tally)
set(gca, 'XTick',(1:size(tally,2)), 'YTick',(1:size(tally,1)))
lix = sub2ind(size(tally), ix2, ix1);
text(ix1,ix2,compose('%d', tally(lix)), 'HorizontalAlignment','center', 'VerticalAlignment','middle')

Another option is the heatmap function.

EDIT — (29 Jan 2021 at 17:31)

Updated plot code.

Answer 2

[Sumera Yamin]

what about using pcolor() command? This can also plot the data as i want

[Star Strider]

The imagesc function and pcolor function are significantly different.

Compare these:

figure
imagesc(tally)
set(gca, 'XTick',(1:size(tally,2)), 'YTick',(1:size(tally,1)))
lix = sub2ind(size(tally), ix2, ix1);
text(ix1,ix2,compose('%d', tally(lix)), 'HorizontalAlignment','center', 'VerticalAlignment','middle')

and:

figure
pcolor(tally)
set(gca, 'XTick',(1:size(tally,2)), 'YTick',(1:size(tally,1)))
lix = sub2ind(size(tally), ix2, ix1);
text(ix1,ix2,compose('%d', tally(lix)), 'HorizontalAlignment','center', 'VerticalAlignment','middle')

The imagesc function is defined by the centres of the squares, the pcolor function is defined by the edges of the squares, so the pcolor plot is one less in each dimension.

[Sumera Yamin]

I see your point now. I tested your code on my script. somehow my matlab complains "Undefined function or variable 'tally'. One more question. with imagesc(), y axis is flipped. I mean it goes from top to bottom, instead of bottom to top. (This is not a problem, just being curious for the reason).