Temperature distribution contour plotting

Here is my task:

A 2D rectangle is heated on one corner and cooled on the other. Create a map of the temperature contours.

Here is my coding to create my grid:

% Defining initial variables

plate_length=60;

plate_height=40;

dx=10;

dy=10;

x = 0:dx:plate_length;

y = 0:dy:plate_height;

nx = length(x); ny = length(y);

%create arrays in y and x

[x_arr, y_arr] = meshgrid(x, y)

%creates array for temperature based on meshgrid size

temp = zeros(ny, nx)

Following this, I have defined the areas of the rectangle that are heated or cooled:

%defining heated points and their temperature

heated_length=20;

heated_top = find((y_arr == 0) & (x_arr <= heated_length));

heated_height=20;

heated_left = find((y_arr <= plate_height-heated_height) & (x_arr == 0));

heated_points = union(heated_top, heated_left);

heated_temp= 100;

temp(heated_points) = heated_temp

%defining cooled points and their temperature

cooled_length=10;

cooled_bottom = find((y_arr == 40) & (x_arr >= plate_length - cooled_length)) ;

cooled_height=10;

cooled_right = find((y_arr >= plate_height - cooled_height) & (x_arr == 60 ));

cooled_points = union(cooled_bottom, cooled_right) ;

cooled_temp= 0;

temp(cooled_points) = cooled_temp

This successfully gives me an array with the correct temperatures on each corner.

Now I must select all of the values in the temp matrix that are not part of the cooled or heated points. How can I do this? My heated points and cooled point are all defined, so how can I say (in code), 'for any point in the temp matrix that isn't a heated or cooled point, it must be set to a set value?'

Thanks Lewis