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# Improper assignment with rectangular empty matrix., how to solve ?

Asked by mounim on 14 Dec 2012

hey everyone

please i am getting this error :

Improper assignment with rectangular empty matrix on this line :

midpoints1(k) = (leftEdge1 + rightEdge1)/2;

how can i solve that ? any help is appreciated, thanks

```for k=700:800
```
`   oneRow1 = binaryImage(k, :);`
```   leftEdge1 = find(oneRow1, 1, 'first');
rightEdge1 = find(oneRow1, 1, 'last');```
`   hold on;`
`   midpoints1(k) = (leftEdge1 + rightEdge1)/2;`
```   plot(leftEdge1, k, 'rx','LineWidth',2);
plot(rightEdge1, k, 'rx','LineWidth',2);```
`   plot(midpoints1(k), k, 'yx','LineWidth',2);`
```end
```
```X1=(700:800);
midpoints1=midpoints1(midpoints1~=0);
new_x1 = linspace(500, 900);
coeffs1 = polyfit(X1, midpoints1, 1);
new_y1 = polyval(coeffs1, new_x1);
plot(new_y1,new_x1, '-','LineWidth',2);
```

mounim on 14 Dec 2012

well, the most appopriate is just to ignore that row, and go on.

Walter Roberson on 14 Dec 2012

What value do you want stored in midpoints1(k) in this situation?

mounim on 14 Dec 2012

it have to just store a zero ( a black pixel ), i tried this code, but it is not working 100% still gives me errors:

```if isempty(midpoints1(k)) then
midpoints1(k)== 0;
end
```

this one not working neither

```if isempty(midpoints1(k)) then
midpoints1(k)= zeros(size(midpoints1(k)));
end
```

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Answer by Walter Roberson on 14 Dec 2012

In some rows, there are no 1's. When that happens, the results of find() are empty. You are trying to store the midpoint of that empty range into midpoints1(k), which requires a location which is a 1x1 value not a 0 x 0 value.

## 1 Comment

Walter Roberson on 14 Dec 2012
```if isempty(leftEdge1)
midpoint1(k) = 0;
else
midpoints1(k) = (leftEdge1 + rightEdge1)/2;
%and do the plotting here
end
```