There is no specific function to do that, but matlab has the next best thing, namely, matrix division. I'll generalize your question. Suppose the two straight lines satisfy the two equations
a*x + b*y = c
d*x + e*y = f
Then their intersection, which is to say the solution to the equations, is given by column vector [x,y] as:
[x;y] = [a b;d e]\[c;f]
Your line parallel to the y-axis is a special case with a = 1, b = 0, and c = some desired constant value of x.
If your lines are determined by pairs of points on the lines, first find their associated equations and then do the above.
