How to know the x projection in this function if the y is known?

How to know the x projection in this function if the y is known? For example If the y = 0.4 what is the x?

xA = 0;
xB = 1;
xf = 1
x  = linspace(0, xf, xf*1e4 + 1);
a  = 9.2;   % 
c  = 0.5;     % center of function
Y  = sigmf(x, [a c]).*((0 <= (x - xA)) & ((x - xA) < (xB - xA)));

Answer 1

[Star Strider]

Use interp1 to interpolate —

xA = 0;
xB = 1;
xf = 1;
x  = linspace(0, xf, xf*1e4 + 1);
a  = 9.2;   % 
c  = 0.5;     % center of function
Y  = sigmf(x, [a c]).*((0 <= (x - xA)) & ((x - xA) < (xB - xA)));

yq = 0.4;
xq = interp1(Y, x, yq)

xq = 0.4559

figure
plot(x, Y)
hold on
plot(xq, yq, 'sr')
hold off
grid
text(xq, yq, sprintf('  \\leftarrow, (%.2f, %.2f)', xq, yq), 'Horiz','left', 'Vert','middle')

.

[M]

@Star Strider Thank you so much

[Star Strider]

As always, my pleasure!

[M]

@Star Strider Can you please check the centroid question of the same shape!

I have mentioned you in the question. Thanks

[Star Strider]

I did, and I just posted an Answer.