How to find value of Y if i know X value from grap

i search on matlab searching question but not found it. I have a graph with a curve. I want to know the Y value from my graph example X = 10 to 11, till 10 to 11 in y axis i have to mark. how to find Y?

i also seen some example like this, i can find for one x value one y value, but continues x data how to mark in cureve

%example having only one x data X = 1:0.1:20;

Y = sin(X);
index = find(X==10);
Y_point = Y(index)
% See graphically
plot(X,Y,X(index),Y_point,'o')

my question is now how to mark for x value 10 to 11

Answer 1

[KSSV]

clc; clear all ;
X = 1:0.1:20;
Y = sin(X);
index = find(X==10);
Y_point = Y(index)
% See graphically
plot(X,Y,X(index),Y_point,'o')
hold on
% plot X in the range 10 to 11
Xi = X(X>=10 & X<=11) ;
Yi = Y(X>=10 & X<=11) ;
plot(Xi,Yi,'*k')

[navi g]

yeah thanku,, to increase number of marker in that range, means now i simulated yuor code, i got like this,

and i need like this more markers like this image

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[afiq hassan]

But what if I want to find value from x axis and I already know the y axis?

[Walter Roberson]

[~, idx] = min( abs(Y_values - target_y_value) );
closest_x = X_values(idx);
closed_y = Y_values(idx);

Answer 2

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/119402-how-to-set-a-marker-at-one-specific-point-on-a-plot-look-at-the-picture#comment_418874