Extraction of values from a graph.

I have drawn a graph witha a few known values. I need the values of the intermediate x-values. The code is as below.

T=20:20:300;
rho=[1000 995 985 974 961 945 928 909 889 867 842 815 786 752 714];
plot(T,rho)

From the above plotted graph I need values of T which are not defined.

If there is any other method through which I can extract values(Not necessarily from the graph like linear interpolation), please do tell.

Thank You.

Answer 1

[J. Alex Lee]

There is a function called "interp1", which seems like it will suit your need. You have options on interpolation method.

T=20:20:300;
rho=[1000 995 985 974 961 945 928 909 889 867 842 815 786 752 714];
plot(T,rho,'.-')

% T values of interest
Ti = [25 56 88 204 288]
rhoi = interp1(T,rho,Ti)

hold on;
plot(Ti,rhoi,'*r')

[Lepakshi Ramkiran]

Thank for the solution, its working.

But if I want more values and i use the following code:

T=20:20:300;
rho=[1000 995 985 974 961 945 928 909 889 867 842 815 786 752 714];
plot(T,rho,'o')
hold on
Ti=20:1000:300;
rhoi=interp1(T,rho,Ti);
hold on
plot(Ti,rhoi,'*r')

The graph is as below:

As you can see the values are not being displayed.

How to rectify this?

[J. Alex Lee]

What do you intend with this line of code:

Ti=20:1000:300;

Uncomment to see the result. You are asking just for the number 20.

If you want 1000 points between 20 and 300 spaced evenly, then do

Ti = linspace(20,300,1000);

[Lepakshi Ramkiran]

yea my bad sorry, got confused.

Thanks. got it.