Error using / Matrix dimensions must agree.

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?

Answer 1

[KSSV]

Check sizes of mass and v2tot, they might not be compatible for matrix multiplication.

[Emanuele Balduzzi]

They are just number, they aren't matrix

[dpb]

Excepting it's the '/' in the error message, not the '*'...

Answer 2

[dpb]

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.