CODEWITHSUNDEEP
matlab
Ben
Ben

Reputation: 1221

Gradient function in matlab gives unexpected result

I find that gradient function in matlab gives me different answer from my expectation.

I tested this dataset

a = [0.337961000000000   0.394426000000000   1.083110000000000;
0.337977000000000   0.394627000000000   1.084470000000000;
0.337972000000000   0.394768000000000   1.085870000000000;
0.337950000000000   0.394923000000000   1.087260000000000;
0.337949000000000   0.395092000000000   1.088510000000000]

According to the way used to calculate gradient

v(2,:) = (a(3,:)-a(1,:))/(2*dt)

where dt = 1/240;

I expect v(2,:) can be 

0.001319999999998   0.041039999999994   0.331200000000011

while gradient function (gradient(a)/dt) give

1.0e+02 *

0.135960000000000   0.895791600000000   1.655623200000000

Can anyone please help to see what is wrong here? Thank you.

Upvotes: 1

Views: 79

Answers (1)

gregswiss
gregswiss

Reputation: 1456

you are looking at the wrong orientation of the gradient, you need to use the second output of gradient.

For example:

[~, fy] = gradient(a);
fy = fy / dt;
fy(2,:)

ans =

     0.0013    0.0410    0.3312

Upvotes: 2

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