# DimensionMismatch ("Cannot Multiply two vectors")

**URL:** <https://discourse.julialang.org/t/dimensionmismatch-cannot-multiply-two-vectors/10989>\
**Category:** General Usage\
**Created:** [May 18, 2018, 1:49pm UTC](https://discourse.julialang.org/t/dimensionmismatch-cannot-multiply-two-vectors/10989 "2018-05-18T13:49:54Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![tfk17lstm](https://avatars.discourse-cdn.com/v4/letter/t/f0a364/32.png) [@tfk17lstm](https://discourse.julialang.org/u/tfk17lstm)\
**Post date:** [May 18, 2018, 1:49pm UTC](https://discourse.julialang.org/t/dimensionmismatch-cannot-multiply-two-vectors/10989/1 "2018-05-18T13:49:54Z")

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Dear Julia users, I am getting the following error when I try to multiply some coefficients contained in my matrix Data G by the values in another matrix P. The code is the following one:

```julia
while bd>dualitygap
q=0;
for i in 1:ngen
 for j in 1:T
## Cases with Popt
 Popt[i,j]=(Lambda[j]-DataG[i,5])/2*DataG[i,4]
 if Popt[i,j]<=DataG[i,2]
 P[i,j]=DataG[i,2]
elseif (Popt[i,j]>=DataG[i,2] && Popt[i,j]<DataG[i,3])
 P[i,j]=Popt[i,j];
 posibles[i,j]=1
elseif Popt[i,j]>=DataG[i,3]
 P[i,j]=DataG[i,3]
 end
## Dynamic Programming
F[i,j]=DataG[i,(4:6)]*[P[i,j]^2;P[i,j];1]-Lambda[j]*P[i,j]
if F[i,j]<0
U[i,j]=1
else
U[i,j]=0
end
end
end >DimensionMismatch("Cannot multiply two vectors")
U
.
.
.

```

Note

```julia
[P[1,1]^2,P[1,1],1]
3-element Array{Float64,1}:
 10000.0
   100.0
     1.0
DatosG[1,(4:6)]
3-element Array{Float64,1}:
   0.002
  10.0
 500.0

```

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<div class="post-metadata">

**Author:** ![rdeits](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/rdeits/32/286_2.png) [@rdeits](https://discourse.julialang.org/u/rdeits)\
**Post date:** [May 18, 2018, 2:08pm UTC](https://discourse.julialang.org/t/dimensionmismatch-cannot-multiply-two-vectors/10989/2 "2018-05-18T14:08:36Z")

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Please post the full error output and try to simplify your example as much as possible. Otherwise there’s no way for us to know what the problem is.

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**Author:** ![StefanKarpinski](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stefankarpinski/32/24_2.png) [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)\
**Post date:** [May 18, 2018, 2:32pm UTC](https://discourse.julialang.org/t/dimensionmismatch-cannot-multiply-two-vectors/10989/3 "2018-05-18T14:32:10Z")

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Although the error is pretty explicit: somewhere you’ve got two vectors and you’re doing `v*w` to multiply them, which does not work. If you want an inner (dot) product of the two, you can do `v'w`. If you want an outer product, you can do `v*w'`. You probably want an inner product.

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<div class="post-metadata">

**Author:** ![ExpandingMan](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/expandingman/32/866_2.png) [@ExpandingMan](https://discourse.julialang.org/u/ExpandingMan)\
**Post date:** [May 18, 2018, 2:59pm UTC](https://discourse.julialang.org/t/dimensionmismatch-cannot-multiply-two-vectors/10989/4 "2018-05-18T14:59:24Z")

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Also can do `v⋅w` for inner product (`\cdot` for the dot).

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<div class="post-metadata">

**Author:** ![tfk17lstm](https://avatars.discourse-cdn.com/v4/letter/t/f0a364/32.png) [@tfk17lstm](https://discourse.julialang.org/u/tfk17lstm)\
**Post date:** [May 21, 2018, 1:18pm UTC](https://discourse.julialang.org/t/dimensionmismatch-cannot-multiply-two-vectors/10989/5 "2018-05-21T13:18:37Z")

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Problem solved, everything is working fine thank you so much.