Error using .* Matrix Dimensions must agree

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Stephanie Goldstein
Stephanie Goldstein am 25 Aug. 2014
Kommentiert: Jan am 4 Jul. 2017
Hello! I am attempting to find the area of grid cells using two vectors, 1)latitude which is 224 X 1 and 2)longitude which is 240 X 1. The code I am using to do so is
R=6371
x=diff(latitude1)
y=diff(longitude)
Area_grid_points=(((2*pi*R)/360)^2).*cos(latitude1).*x.*y
Unfortunately when I use this code I receive the error "Error using .* Matrix Dimensions must agree." I am assuming that I receive this error because cos(latitude1) produces an array of 224*1 which is different than that produced by diff(longitude1) which is 240 X 1. Can anyone direct me in the right direction to correct this discrepancy? Thanks so much!

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Antworten (3)

Kelly Kearney
Kelly Kearney am 25 Aug. 2014
Well, diff is always going to return a result 1 element shorter than the input, since it's measuring the distance between elements. In your case, you'll have to decide what latitude you want to correspond to each grid cell: top? bottom? middle?
I usually choose the midpoint for things like this:
R=6371
x=diff(latitude1)
y=diff(longitude)
latmid = (latitude(1:end-1)+latitude(2:end))./2;
Area_grid_points=(((2*pi*R)/360)^2).*cos(latmid).*x.*y;
  3 Kommentare
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Stephanie Goldstein
Stephanie Goldstein am 25 Aug. 2014
Hi Kelly. Thanks for your response. Unfortunately, I still received the error "Error using .* Matrix dimensions must agree." Do you know how I can make the matrix dimensions equal to one another?
Kelly Kearney
Kelly Kearney am 25 Aug. 2014
Bearbeitet: Kelly Kearney am 25 Aug. 2014
I was assuming that lattitude and longitude were the same size, but apparently not. Assuming that both latitude and logitude are row vectors, representing the edges of a rectangular (in lat/lon space) region, perhaps you want:
R = 6371
x = diff(latitude1);
y = diff(longitude);
latmid = (latitude(1:end-1)+latitude(2:end))./2;
Area_grid_points = (2*pi*R/360)^2 .* y' * (cos(latmid).* x);
Note that my use of matrix multiplication with a column and row vector is a shortcut for expanding the two vectors into a full grid.

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José-Luis
José-Luis am 25 Aug. 2014
Bearbeitet: José-Luis am 25 Aug. 2014
If you want element by element multiplication you should use .* instead of *. whether you want this or matrix multiplication, the number of elements and size of your array should be congruent.
Maybe you are looking for something like bsxfun() instead:
bsxfun(@times, latitude, longitude')
  2 Kommentare
Stephanie Goldstein
Stephanie Goldstein am 25 Aug. 2014
Hi Jose-Luis. I tried using .* and received an error of "Error: Unexpected MATLAB operator." Here is what I really need help on: how can I make the number of elements and size of my arrays congruent? Also, can you please explain to me what bsxfun(@times, latitude, longitude') does? Thanks so much.
José-Luis
José-Luis am 25 Aug. 2014
Well, I don't know. How do you get the latitude and longitude vectors in the first place.
doc bsxfun

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Sajjad Ali
Sajjad Ali am 4 Jul. 2017
Bearbeitet: Sajjad Ali am 4 Jul. 2017
I am also getting error Error using . Matrix dimensions must agree.* in following line of code _[m,n]=size(thick_image(:,:,1));
indTerm=sub2ind([m,n],CentroidTerm(:,1),CentroidTerm(:,2));
Z=zeros(m,n);
Z(indTerm)=1;
ZTerm=Z.*ROI';
[CentroidTermX,CentroidTermY]=find(ZTerm);_ can any one help me to resolve this issue?
  2 Kommentare
Walter Roberson
Walter Roberson am 4 Jul. 2017
You do not say what size of ROI is
Jan
Jan am 4 Jul. 2017
Please create a new thread for a new question and remove this message here. Otherwise it gets unclear to which question an answer belongs and the Accepted status is meaningless. Thanks.

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