Intersection between line and function

hello i draw graphics on matlab based on data found in tables, and what i'm trying to do is project a Y value and find its equivalent X, i give you the code used to create the projection Y, as well as the graph

xlim([0,50])

YV = [min(X1)-0.1:0.01:max(X1)+0.1];

XVmax = zeros(1,numel(YV));

j = [1:numel(YV)];

XVmax(j)= max(Y2_max);

plot(YV,XVmax,'--m')

Answer 1

[jonas]

Use InterX from fileexchange for high accuracy even with low resolution data. Example:

%%Some data
x=0:.9:20;
y=x.^2
%%Set threshold
t=200;

yt=[t t]
xt=[min(x),max(x)];
P=InterX([xt;yt],[x;y])
h=plot(x,y,'+-k',...
    xt,yt,'r',...
  P(1),P(2),'bo')    

set(h(3),'markerfacecolor',[1 0 0])

Note that the resolution of the x-range is quite poor, yet the intercep is accurate.