about gradient and diff

13 views (last 30 days)
Yuji Zhang
Yuji Zhang on 15 Jun 2013
The help of my matlab says: (in article "gradient -Gradient vector of scalar function")
-If x is a scalar, gradient(f,x) = diff(f, x).
This is wrong, right?
diff(f,2) should = diff( diff(f) ) % means 2nd order diff
while gradient (f, 2) means the grid increment is 2. which means, for a curve f-t, or f(t), t is a linear space and dt = t(2)-t(1) = 2
Let me know everybody~ Thanks~
  5 Comments
Image Analyst
Image Analyst on 15 Jun 2013
How do you tell your code which one to use?
Yuji Zhang
Yuji Zhang on 15 Jun 2013
Edited: Yuji Zhang on 15 Jun 2013
I think, if your input y is a symbolic function, like y = x^2, then gradient(y) is symbolic gradient.
If the y is a numerical curve, like y = [1 2 3 4 ....]; then gradient(y) is the numerical gradient.

Sign in to comment.

Accepted Answer

Walter Roberson
Walter Roberson on 15 Jun 2013
Symbolic gradient, http://www.mathworks.com/help/symbolic/gradient.html, is the gradient vector of a scalar function, but numeric gradient, http://www.mathworks.com/help/matlab/ref/gradient.html is just "Numerical gradient". It is numerical gradient for which the "2" would mean a point spacing of 2, and it is the symbolic gradient for which the "2" would mean double differentiation.
  1 Comment
Yuji Zhang
Yuji Zhang on 15 Jun 2013
Hi Walter~
Nice explanation! Thank you so much! I didn't know there were two different gradient functions. Yea, I see - makes sense. These two gradient functions are in different contexts.
Thanks again~

Sign in to comment.

More Answers (0)

Categories

Find more on Symbolic Math Toolbox in Help Center and File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!