Meaning of the symbol '' \ ''

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Waqas Syed
Waqas Syed on 28 Jul 2015
Edited: Bruno Luong on 1 Oct 2021
Hi,
I am trying to understand a pre written matlab code. There is a line: dx = -(J \ F);
What does the forward slash mean? Does it mean F divided by J or something?

Accepted Answer

Lukas Bystricky
Lukas Bystricky on 28 Jul 2015
Edited: Lukas Bystricky on 28 Jul 2015
That's actually a backward slash. J\F is equivalent to solving the system J dx = F for dx, where J is a matrix (probably a Jacobian) and F and dx are vectors.
  16 Comments
Bruno Luong
Bruno Luong on 1 Oct 2021
@Walter Roberson: "So J\F vs F/J would only be the same if F and J are each real and symmetric."
Not true
J=rand(3); J=J+J',
J = 3×3
0.0670 0.8628 0.2369 0.8628 1.6893 1.1714 0.2369 1.1714 1.6260
F=rand(3); F=F+F',
F = 3×3
0.8988 0.3888 0.1346 0.3888 0.2691 0.9150 0.1346 0.9150 1.4615
J\F
ans = 3×3
-1.1987 -1.0761 -0.0648 1.3265 0.4196 -0.1101 -0.6982 0.4172 0.9877
F/J
ans = 3×3
-1.1987 1.3265 -0.6982 -1.0761 0.4196 0.4172 -0.0648 -0.1101 0.9877
Bruno Luong
Bruno Luong on 1 Oct 2021
Edited: Bruno Luong on 1 Oct 2021
@Kriti Salwan "What happens if we are applying backlash to a matrix which is not square ?"
x = A\b;
Otherwise it's a least square solution
x = argmin(norm(A*x-b))
or equivalently
x = pinv(A)*b

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