Asked by Vivek
on 3 Jan 2013

This is what my program to create a graph.. now i want to read the graph and it has to produce the y value for my input x value. is there any syntax for that?

j=input('Enter the number of straight lines in the graph: ');

for i=1:j

disp('Enter the X Y co-ordinate of one end of the straight line:');

x1(i)=input(' ');

y1(i)=input(' ');

disp('Enter the X Y co-ordinate of another of the straight line:');

x2(i)=input(' ');

y2(i)=input(' ');

c(i)=input('Enter the Y-intercept for straight line: ');

m(i)=(y2(i)-y1(i))/(x2(i)-x1(i));

end

for i=1:j

x=x1(i):0.01:x2(i);

y=((m(i))*x)+c(i);

plot(x,y);%,'MarkerFaceColor','g');

hold on;

%axis([-10 10 -5 5])

end

disp('-----------------------');

disp('your graph is displayed');

disp('-----------------------');

disp('Enter the X value from your graph: ');

p=input(' ');

disp('Corresponding Y is: ');

Answer by Davide Ferraro
on 3 Jan 2013

Accepted Answer

Why are you asking two (x,y) values for a line and then also the intercept? Given two points you are able to calculate both m and c. And that point you will have the equation y of your line that you can evaluate to find the corresponding Y.

If you have more lines you may consider including and IF-ELSE statement, check what is the X value, associate it to the corresponding equation and then evaluate the equation. As Walter pointed out you may have multiple Y values, you may prevent this by checking that the user is using different X ranges when creating the curves.

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Answer by Dr. Seis
on 3 Jan 2013

Edited by Dr. Seis
on 3 Jan 2013

Disregarding the fact that you can determine your c value from your m value, x1 value, and y1 value (or m, x2 and y2)... I think the syntax you are looking for (following your current syntax) is something like:

new_y = ... ; % Determine new y value for input x value

disp(sprintf('Corresponding Y is: %f',new_y));

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## 2 Comments

## Walter Roberson (view profile)

## Direct link to this comment

https://www.mathworks.com/matlabcentral/answers/57861-it-is-possible-to-read-the-graph-and-it-has-to-produce-the-y-value-for-my-input-x-value#comment_120391

## Vivek (view profile)

## Direct link to this comment

https://www.mathworks.com/matlabcentral/answers/57861-it-is-possible-to-read-the-graph-and-it-has-to-produce-the-y-value-for-my-input-x-value#comment_120586

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