# Subtracting a Vector from a Scalar-Multiplied Matrix

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Commenté : Paul le 5 Avr 2024
Let's say that we have the following two matrices and we want to calculate . We know that it is not defined, but MATLAB gives me the following result.Could anyone explain me why that happens?
C=[1 2; 2 1]
C = 2x2
1 2 2 1
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E=[1;2]
E = 2x1
1 2
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3*C-E
ans = 2x2
2 5 4 1
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##### 5 commentairesAfficher 3 commentaires plus anciensMasquer 3 commentaires plus anciens
@Torsten Yes this is my problema tha it is defined in Matlab but not in Maths.
This is what I want to show to my students
Torsten le 5 Avr 2024
It's just a convention to get rid of the bsxfun - there is nothing to explain (or even justify).

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### Réponse acceptée

Steven Lord le 4 Avr 2024
##### 8 commentairesAfficher 6 commentaires plus anciensMasquer 6 commentaires plus anciens
Oh ok!! Now it is all clear! Thank you!
Paul le 5 Avr 2024
Even prior to R2016B, as far back as to the very first release as far as I know, Matlab implemented scalar expansion. Code like this has always worked
eye(2) - 1
ans = 2x2
0 -1 -1 0
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even though subtracting a scalar from a matrix is not mathematically rigorous.

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