# Find a y axis increasing point in a plot -

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Khaled Genidy on 21 Oct 2021
Answered: Star Strider on 21 Oct 2021
This is a similar graph to what i have.
keeping in mind the values of Y-axis always changes differently when i run the script on different data
What code do i need to add to find the exact begining point of the Y-axis when increasing at (-1) at point of X-axis
and find the exact point of it Y-axis when it reach (1) in x axis.
Is it possible to give out the subtraction point of X(2)-X(1) and presented in [legend]
unfortunatly i dont want to use any of the figure functions

Star Strider on 21 Oct 2021
Try something like this —
x1 = -2:2;
y1 = [0 0 1 0 0];
x2 = linspace(-2, 2);
y2 = interp1(x1, y1, x2);
[maxy2,idx2] = max(y2);
XP(1) = find(diff(y2(1:idx2))>0, 1, 'first')+1;
XP(2) = find(diff(y2(idx2+1:end))==0, 1, 'first')+idx2;
figure
plot(x1,y1,'-b')
hold on
plot(x2, y2, '--g', x2(XP), zeros(size(XP)),'+r')
hold off
text(x2(XP),[0 0], compose('\\leftarrow %.1f',x2(XP)), 'Horiz','left', 'Vert','middle', 'Rotation',90)
Since I have no idea how continuous the actual data are, I interpolated them here to find the points-of-interest with higher resolution.
.

KSSV on 21 Oct 2021
idx = find(y==1) ;
iwant = idx(1)-1

R2020a

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