Error using / Matrix dimensions must agree.

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Emanuele Balduzzi
Emanuele Balduzzi 2016-12-15
编辑： dpb 2016-12-15
Hi everyone! I'm new, and I've got this problem:
_Error using /
Matrix dimensions must agree.
Error in viniz (line 58)
Teff=11603*mass*v2tot/(3*nat);_
I write my simple code:
function [vx0 vy0 vz0] = viniz
global nat tempiniz mass
vx0=zeros(nat,1);
vy0=zeros(nat,1);
vz0=zeros(nat,1);
v0=zeros(nat,1);
cost=sqrt(3*tempiniz/(11603*mass));
%Creo velocità
for i=1:nat
vx0(i)=cost*(2*rand-1);
vy0(i)=cost*(2*rand-1);
vz0(i)=cost*(2*rand-1);
end
%Calcolo velocità media
vxmed=0;
vymed=0;
vzmed=0;
for i=1:nat
vxmed=vxmed+(vx0(i)/nat);
vymed=vymed+(vy0(i)/nat);
vzmed=vzmed+(vz0(i)/nat);
end
%Riscalo velocità
for i=1:nat
vx0(i)=vx0(i)-(vxmed);
vy0(i)=vy0(i)-(vymed);
vz0(i)=vz0(i)-(vzmed);
v0(i)=((vx0(i)*vx0(i))+(vy0(i)*vy0(i))+(vz0(i)*vz0(i)))^(1/2);
end
% Calcolo T efficace
v2tot=0;
for i=1:nat
v2tot=v2tot+(v0(i)*v0(i));
end
Teff=11603*mass*v2tot/(3*nat);
%Riscalo con Teff sotto radice così velocità delle mia particella
%corrisponde a tempiniz
for i=1:nat
vx0(i)=vx0(i)*((tempiniz/Teff)^(1/2));
vy0(i)=vy0(i)*((tempiniz/Teff)^(1/2));
vz0(i)=vz0(i)*((tempiniz/Teff)^(1/2));
end
end
Can anyone help me?

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回答（2 个）

KSSV
KSSV 2016-12-15
Check sizes of mass and v2tot, they might not be compatible for matrix multiplication.
  2 个评论
dpb
dpb 2016-12-15
Excepting it's the '/' in the error message, not the '*'...

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dpb
dpb 2016-12-15
编辑：dpb 2016-12-15
global nat tempiniz mass
is very bad inside the function; you can screw up what they are too easily. Make them arguments to the function.
IF nat is a scalar constant as it appears your code assumes, then the line above will not error on the divide operation; anything can be operated on by a constant. Hence, something broke other than what you've shown us; we can't see the data in the workspace at the time of the evocation.
Also, the function could be written without looping it appears...
vx0=zeros(nat,1);
...
for i=1:nat
vx0(i)=cost*(2*rand-1);
...
is simply written in Matlab as
vx0=cost*(2*rand(nat,1)-1);
and similarly for the other terms and loops.

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