Question

I have an array:

step1 = [0,0;
         0,1;
         1,1;
         2,3;
         3,4;
         3,5;
         3,6;
         3,7;
         4,7;
         5,7;
         6,7;
         6,6;
         6,5;
         6,4;
         6,3;
         6,2;
         5,1];

I want to step through this array and create new arrays for the row and column that increment by 0.1 from one row to another. This is what I did:

z=1;
u=length(step1);
step_b4X = zeros(u,1);
step_b4Y = zeros(u,1);
while z <= length(step1)
    step_b4X = step_presentX;
    step_presentX(z,1) = step1(z,1);
    step_b4Y = step_presentX;
    step_presentY(z,1) = step1(z,2);
    pathX = step_b4X:0.1:step_presentX;
    pathY = step_b4Y:0.1:step_presentY;
    z = z+1;
end

I get zeros.
I want pathX = 0:0.1:0….pathY = 0:0.1:1
next pathX = 0:0.1:1….pathY = 1:0.1:1… and so on

Answer 1

If you do

start:increment:end

where start == end, you’ll get a scalar equal to start (which is logical).

If you want pathX and pathY to have the same length at each iteration, you’ll have to do this:

z = 1;
while z <= length(step1)

    currentX = step(z,1);   nextX = step(z+1,1);
    currentY = step(z,2);   nextY = step(z+1,2);

    pathX = currentX : 0.1 : nextX;
    pathY = currentY : 0.1 : nextY;

    if numel(pathX) == 1
        pathX = repmat(pathX, numel(pathY),1); end
    if numel(pathY) == 1
        pathY = repmat(pathY, numel(pathX),1); end

    z = z+1;
end

Now you’ll have the right arrays at each iteration, that you’ll use directly or save in a cell-array for later. If you want everything in one big array, add this to the end of the loop:

    pathX_final = [pathX_final; pathX];
    pathY_final = [pathY_final; pathY];

and initialize them as empty before the loop, of course.

Alternatively (much cleaner and possibly a bit faster), ditch the whole loop and use interp1:

x = step1(:,1);
y = step1(:,2);

xx = interp1(1:numel(x), x, 1:0.1:numel(x));
yy = interp1(1:numel(y), y, 1:0.1:numel(y));