How to expand a summation with different indexes
1 visualización (últimos 30 días)
Mostrar comentarios más antiguos
How to expand a summation with different indexes like this?
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/149648/image.jpeg)
Any help would be appreciated.
4 comentarios
Respuestas (4)
Thorsten
el 2 de Oct. de 2015
sum(diff(f(1:4)).*n(1:3).*arrayfun(@(x) sum(m(x:end)), 3:5))
7 comentarios
Muthu Annamalai
el 2 de Oct. de 2015
@Thorsten : nice solution exploiting fact that each sum is independent of the other index, i and j, we may use dot products to compute the inner loop, and repeat it again for index i. I wonder if there is also a way to do it with mesgrid() and matrix products.
Sean de Wolski
el 2 de Oct. de 2015
Editada: Sean de Wolski
el 2 de Oct. de 2015
sum(diff(f(1:4)).*n(1:3).*sum(m(3:5)))
5 comentarios
Thorsten
el 2 de Oct. de 2015
Editada: Thorsten
el 2 de Oct. de 2015
Sean, yes, i is 1:3, so the starting index of j is 3:5, so the sum runs for j = 3:5 for i = 1, j = 4:5 for i = 2, and j = 5 for i = 3, i.e., assumes values sum(m(3:5)), sum(m(4:5)) and sum(m(5)) for i=1,2,3. You forgot to sum over the different m(j), as far as I can see.
Ver también
Categorías
Más información sobre Matrix Indexing en Help Center y File Exchange.
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!