How can I use a vector value as a row index to modify an element?

I have a matrix X (363x8760) with values (real numbers) and another vector V (1x8760) with values (1-363) that indicate a specific row for each column in matrix X. Additionally I have a vector P (1x8760) that contains percentage values (0-1). I need to create a matrix Y (363x8760) equal X expect all values below the row indicated by V are now 0 and the value in the row indicated by V is equal to the original value multiplied by the percentage value.

For example

X = [10 20 50; 30 40 50; 10 20 10]

V = [1 2 3]

P = [.5 .25 .75]

I would want Y to look like

Y = [5 0 0; 30 10 0; 10 20 7.5]

Answer 1

[James Tursa]

Y = X;
m = (1:size(X,1))'; % Generic row index vector
g = bsxfun(@lt,m,V); % Logical indexes of the 0's
Y(g) = 0;
g = bsxfun(@eq,m,V); % Logical indexes of the percents
Y(g) = Y(g).*P(:);

Assumes all the values of V are valid row indexes, and the various variable sizes are compatible, etc.