Plotting plain grid of size 100 X 100 AND selecting a "block" in the grid

I'm trying to plot a plain grid of a certain size. The regular " grid on " function gives me an automatic 1 X 1 grid.

I'm trying to plot a grid that is 100 X 100 and having each block a size of 1 X 1. This is what I have attempted so far:

x = (0:1:100)
y = (0:1:100)
fig1 = plot(x,x)
grid on
xlabel('x-axis')
ylabel('y-axis')

This is what it outputs

I'd like to output this grid without the line y=x showing up on it.

Also, I am trying to figure out how to select a specific block on the grid. I know that I can select a specific point on the grid but how would I be able to "shade in" an exact block on the grid.

Answer 1

[Star Strider]

Try this:

figure(1)
plot([0:100; 0:100], [0:100; 0:100], 'k')
hold on
fill([0 1 1 0]+50, [0 0 1 1]+50, 'r')               % Colour (50,50) Red
hold off
hax = gca;
hax.XTick = 0:100; 
hax.YTick = 0:100;
hax.XTickLabel = [];
hax.YTickLabel = [];
grid
axis square

[Ammar Babikir]

Got it. Thank you!

[Star Strider]

As always, my pleasure!

[Star Strider]

The annotated version —

figure(1)                                           % Set ‘figure’ Object
plot([0:100; 0:100], [0:100; 0:100], 'k')           % Initial Plot Call
hold on                                             % Set To Plot Multiple Plots In Same Axes
fill([0 1 1 0]+50, [0 0 1 1]+50, 'r')               % Colour (50,50) Red <—————
hold off                                            % Stop Plotting Multiple Plots In Same Axes
hax = gca;                                          % Get Current ‘axes’ Handle
hax.XTick = 0:100;                                  % Set X-Tick Locations
hax.YTick = 0:100;                                  % Set Y-Tick Locations
hax.XTickLabel = [];                                % ‘Turn Off’ Default X-Tick Labels
hax.YTickLabel = [];                                % ‘Turn Off’ Default Y-Tick Labels
grid                                                % Show Grid
axis square                                         % Set Square Axes For Aesthetic Purposes

[Ammar Babikir]

I appreciate your help. I actually have a few questions regarding your annotations:

1) why do you put 'k' when you're plotting the X vs Y matrices? I took it out and it still gave me the same result. Is there significance behind using 'k'?

2) When using "fill", how do you "read" the location of the center box? You have four numbers in the matrix [ 0 1 1 0 ] and then [ 0 0 1 1 ]. I understand that 'r' is the color code. But, why is "+50" important?

[Star Strider]

The 'k' colors the initial plot black. I just wanted to specify that in the plot call.

The fill (and related patch) functions require that the area to be filled be specified as a border. So here it plots from (0,0) to (1,0) to (1,1) to (0,1). The function closes the curve itself. The ‘50’ values offset this to the desired square, so add 50 to the respective coordinates to define the square being colored in that fill call. Replace the 50 by any (x,y) values you want, to color a particular square. So:

fill([0 1 1 0]+31, [0 0 1 1]+76, 'r')

will color the square at (31,76).

[Ammar Babikir]

I see. Also, when you use "hax" to plot the axes and the X and Y-axis ticks, is "hax" an actual library in MATLAB? I tried looking it up in documentation but I didn't really find anythijng. In this specific case, you use hold on, fill the square, and then hold off. When I removed the on and off from the hold functions, it didn't change anything about the plot. Is there any significance in using the "on" and "off" for the holds?

[Star Strider]

The ‘hax’ variable is the handle to the axes object created with the initial plot call. See the documentation on Axis Properties (link) for a full description.

The hold calls permit plotting more objects (here the fill call) on the same axes. I use ‘hold on’ and ‘hold off’ to keep track of the hold state. Without the ‘on’ and ‘off’ designators, hold simply toggles the hold state.

[Evangelos Rompogiannakis]

If i want to fill all the blocks where y < x how can i do it ??

Answer 2

[KSSV]

x = (0:1:100) ;
y = (0:1:100) ;
% fig1 = plot(x,x)
[X,Y] = meshgrid(x,y) ;
mesh(X,Y,'edgecolor','k')
view(2)
grid on
xlabel('x-axis')
ylabel('y-axis')

[Ammar Babikir]

I actually don't want any color on the grid. Would it be possible to just get that same grid that I had just without the line going through it?

[KSSV]

You can set edgecolor property to black. Edited it.