Why does gradient function calculates wrong dimensions?
조회 수: 2 (최근 30일)
이전 댓글 표시
Hi there,
Why does the gradient function calculates the first two dimensions wrong?
Example:
[mshx,mshy,mshz] = ndgrid(0:.1:10,0:.1:10,0:.1:10);
[gxx,gyx,gzx] = gradient(mshx);
[gxy,gyy,gzy] = gradient(mshy);
[gxz,gyz,gzz] = gradient(mshz);
Here all gij are zero except for gyx, gxy, gzz. But how can I calculate the gradient more consistently so that all gij are zero except for gxx, gyy, gzz?
Thank you for your help.
Best regards
Michael
댓글 수: 0
채택된 답변
Ameer Hamza
2020년 4월 30일
편집: Ameer Hamza
2020년 4월 30일
Use meshgrid instead of ndgrid
[mshx,mshy,mshz] = meshgrid(0:.1:10,0:.1:10,0:.1:10);
[gxx,gyx,gzx] = gradient(mshx);
[gxy,gyy,gzy] = gradient(mshy);
[gxz,gyz,gzz] = gradient(mshz);
댓글 수: 3
Stephen23
2020년 4월 30일
편집: Stephen23
2020년 4월 30일
Note that using meshgrid is not a general solution, it fails for N==1, i.e. when the input is a vector:
>> mshx = meshgrid(0:10);
>> gradient(mshx) % oops!
ans =
1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1
1 1 1 1 1 1 1 1 1 1 1
It could be made to work by providing the first input argument as a scalar and the second as the vector, but that requires special-case handling. This is not just a theoretical problem: it will be relevant if you write a general solution for any N, e.g. with comma-separated lists as to provide the inputs/outputs of the gridding function and calling gradient in a loop on the outputs.
The solution I gave in my answer to your other (identical) question works for all N, no special cases.
추가 답변 (0개)
참고 항목
카테고리
Help Center 및 File Exchange에서 Creating and Concatenating Matrices에 대해 자세히 알아보기
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!