Here is the code:
syms x y
My expression looks like a sum of three parts P1, P2 and P3. fimplicit always draws a straight line like y=P_in. I see, that Mathlab writes that x and y values are "1x1 sym". I think, there is a mistake. My x should changes from 0 to 20 with some step (step doesn't matter). I tryed to write "x=0:0.1:20;" before the expression for f(x,y), but Mathlab wrote: "Invalid indexing or function definition. Indexing must follow MATLAB indexing. Function arguments must be symbolic variables, and function body must be sym expression". Also I tryed to write in expression for fimplicit: fimplicit(f [0 20 0 10]) but it only caused a changing of axes, but the graph still looked like a line.
How can I fix this problem? The graph should be a curve, not a straight line