I often need to plot 10 images together, but using this code results in small images : 

img = rand(400,600); 
for i=1:10
 subplot(2,5,i); 
 imshow(img); 
 title(['Image ' int2str(i)]); 
end

As you can see, the images do not use all available space in the screen. How can I increase the size, or decrease the padding/margin between them? 

Thanks for any help. 

In MATLAB, the size of a subplot within a figure can be controlled using the Position property of the subplot. The Position property is a four-element vector [left bottom width height] that specifies the size and location of the subplot within the figure, where the values are given in relative units ranging from 0 to 1.

Here is an example of how to set the size of a subplot in a figure in MATLAB: 

figure;
subplot(2,2,1);
plot(1:10);
title('Plot 1');

% Set the size of subplot 1
subplot(2,2,1);
set(gca,'Position',[0.1 0.55 0.35 0.35]);

In this example, the subplot is set to occupy 35% of the figure width and 35% of the figure height, with the lower left corner located 10% from the left and 55% from the bottom of the figure. You can adjust the values in the Position vector to control the size and location of the subplot.

It is also possible to control the size of subplots using the subplot function by specifying the dimensions of the subplot as arguments. For example, to create a subplot that spans two columns and one row, you can use the following code: 

subplot(2,2,[3,4]);
plot(1:10);
title('Plot 2');

This creates a subplot that takes up the bottom two subplots in a 2x2 grid of subplots.