# Why for loop doesn't work in my code

**URL:** <https://discourse.julialang.org/t/why-for-loop-doesnt-work-in-my-code/65567>\
**Category:** Modelling & Simulations\
**Tags:** question\
**Created:** [July 30, 2021, 8:14pm UTC](https://discourse.julialang.org/t/why-for-loop-doesnt-work-in-my-code/65567 "2021-07-30T20:14:22Z")\
**Posts on this page:** 5\
**Page:** 2

<div class="post-metadata">

**Author:** ![DNF](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/dnf/32/10191_2.png) [@DNF](https://discourse.julialang.org/u/DNF)\
**Post date:** [August 4, 2021, 7:44pm UTC](https://discourse.julialang.org/t/why-for-loop-doesnt-work-in-my-code/65567/22 "2021-08-04T19:44:17Z")

</div>

Your `Y` matrix is still wrong. And what about `R`? And, as @zdenek_hurak said, fix the slash.

You must look carefully over every line of your code, please. Every last thing must be correctly translated.

---

<div class="post-metadata">

**Author:** ![sajad\_ghassemi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sajad_ghassemi/32/25241_2.png) [@sajad\_ghassemi](https://discourse.julialang.org/u/sajad_ghassemi)\
**Post date:** [August 7, 2021, 7:44pm UTC](https://discourse.julialang.org/t/why-for-loop-doesnt-work-in-my-code/65567/23 "2021-08-07T19:44:22Z")

</div>

I checked my code again and again . Thanks for the reply and reminding me about my silly mistake but the figures of MATLAB and Julia are not the same

```julia
using Plots
plotly()
Plots.PlotlyBackend()
currentcap=zeros(1,250001);
voltagecap=zeros(1,250001);
currentind=zeros(1,250001);
V= zeros(9,250004);
t_end = 250e-3;
dt = 1e-6;
t = 0:dt:t_end;
vp=20;
freq=50;
vs = vp*sin.(2*π*freq.* t')
L=1e-3;
R=10000;
C=1e-6;
Roff=10^10;
a=0; b=1; f=0; g=1; c=0; e=1; h=0; n=1;
  for i=2:250001
         Y = [dt/L -dt/L 0 0 1 0 0 0 0 
             -dt/L dt/L+1/Roff -c/Roff -a/Roff 0 1 0 0 -1
              0 -c/Roff (1/R)+(C/dt)+1/Roff -1/R-C/dt 0 -1 -1 0 0
              0 -a/Roff -1/R-C/dt 1/R+C/dt+1/Roff 0 0 0 1 1
              1 0 0 0 0 0 0 0 0
              0 a -a 0 0 b 0 0 0
              0 0 -c 0 0 0 e 0 0
              0 0 0 -f 0 0 0 g 0
              0 -h 0 h 0 0 0 0 n];
              x1=V[5,i]-currentind[1,i-1]; x2=currentind[1,i-1]-V[6,i]+V[9,i]; x3=V[6,i]-currentcap[1,i-1]+V[7,i]; x4=currentcap[1,i]-V[8,i]-V[9,i] ;
              A =[x1
                  x2
                  x3
                  x4
                  vp*sin.(2*π*freq.*t'[1,i])
                  0
                  0
                  0
                  0];
                x=A\Y;
                V[:,i]=x;
                currentcap[1,i]=(C/dt)*(V[3,i]-V[3,i-1]-V[4,i]+V[4,i-1]);
                 voltagecap[1,i]=V[3,i]-V[4,i];
                currentind[1,i]=(dt/L)*(V[1,i]-V[2,i]+V[1,i-1]-V[2,i-1])+currentind[1,i-1];
                if V[2,i]-V[3,i]>0 || V[6,i]>0
                   a=1;b=0;
                elseif V[6,i]<=0
                     a=0; b=1;
                else
                  a=0; b=1;
                end
                
                if -V[3,i]>0 || V[7,i]>0
                   c=1; e=0;
                elseif V[7,i]<=0
                     c=0; e=1
               else
                    c=0; e=1;
                end
               if V[4,i]>0 || V[8,i]>0
                  f=1; g=0;
               elseif V[8,i]<=0
                  f=0; g=1
               else
                  f=0; g=1;
               end
               if V[4,i]-V[2,i]>0 || V[9,i]>0
                  h=1; n=0;
               elseif V[9,i]<=0
                  h=0; n=1
               else
                  h=0; n=1;
               end
   end

voltagecap=voltagecap';
plot(t,voltagecap)

```

the plot is as follows:  
 ![error](https://global.discourse-cdn.com/julialang/original/3X/e/5/e5b866a3355d3c89b52da6dbffae72e82a48489c.png)  
but the figure of Matlab is like this:  
 ![error](https://global.discourse-cdn.com/julialang/original/3X/1/7/17b0439edbfbe633750ab305b9517a84685bc9f5.png)

---

<div class="post-metadata">

**Author:** ![sajad\_ghassemi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sajad_ghassemi/32/25241_2.png) [@sajad\_ghassemi](https://discourse.julialang.org/u/sajad_ghassemi)\
**Post date:** [August 7, 2021, 7:52pm UTC](https://discourse.julialang.org/t/why-for-loop-doesnt-work-in-my-code/65567/24 "2021-08-07T19:52:26Z")

</div>

Thanks for the reply,  
I corrected the Matrix and the value of R but still the output of my code in Julia is not correct

---

<div class="post-metadata">

**Author:** ![zdenek\_hurak](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/zdenek_hurak/32/53118_2.png) [@zdenek\_hurak](https://discourse.julialang.org/u/zdenek_hurak)\
**Post date:** [August 7, 2021, 8:44pm UTC](https://discourse.julialang.org/t/why-for-loop-doesnt-work-in-my-code/65567/25 "2021-08-07T20:44:08Z")

</div>

Your linear equation inside the code is still not set up correctly. In your original Matlab code, you form a matrix `Y` and a column vector `I`. You then go ahead and solve the equation `Yx=I` for a vector `x`. In your code you do it by computing the inverse of the matrix as in `x=inv(Y)*I`, which is not a recommendable way from a numerical point of view, and therefore you were advised to use backslash. The same recommendation to avoid explicit computation of the inverse holds in Julia. And coincidently, the same syntax with backslash is used in Julia. You were even given the particular code: `x = Y\I`. Why did not you just use it?

Instead, in your new code I can observe that you just renamed your vector `I` to `A` and now you try to solve the set of linear equations by writing `x=A\Y`, which sends you back to your previous (incorrect) solution `x = I\Y`.

Perhaps there is some misunderstanding as for what the backslash means here. If you do not find the usage of the symbol intuitive, have a look at the [documentation for backslash](https://docs.julialang.org/en/v1/base/math/#Base.:%5C-Tuple%7BAny,%20Any%7D). If you want to solve `Ax=b` for `x`, given some matrix `A` and (column) vector `b`, you just write `x=A\b`. But this is identical to [Matlab syntax](https://www.mathworks.com/help/matlab/ref/mldivide.html).

---

<div class="post-metadata">

**Author:** ![sajad\_ghassemi](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/sajad_ghassemi/32/25241_2.png) [@sajad\_ghassemi](https://discourse.julialang.org/u/sajad_ghassemi)\
**Post date:** [August 8, 2021, 2:59pm UTC](https://discourse.julialang.org/t/why-for-loop-doesnt-work-in-my-code/65567/26 "2021-08-08T14:59:31Z")

</div>

I edited the Y\A but I don’t know why the code never enters the loop. It’s so strange. This is my first problem.

```julia
using Plots
plotly()
Plots.PlotlyBackend()
currentcap=zeros(1,250001);
voltagecap=zeros(1,250001);
currentind=zeros(1,250001);
V= zeros(9,250004);
t_end = 250e-3;
dt = 1e-6;
t = 0:dt:t_end;
vp=20;
freq=50;
vs = vp*sin.(2*π*freq.* t')
L=1e-3;
R=10000;
C=1e-6;
Roff=10^10;
c1=0;
a=0; b=1; f=0; g=1; c=0; e=1; h=0; n=1;
i=2;
for i=2:250001
    c1=c1+1;
 Y = [dt/L -dt/L 0 0 1 0 0 0 0
     -dt/L dt/L+1/Roff -c/Roff -a/Roff 0 1 0 0 -1
      0 -c/Roff (1/R)+(C/dt)+1/Roff -1/R-C/dt 0 -1 -1 0 0
      0 -a/Roff -1/R-C/dt 1/R+C/dt+1/Roff 0 0 0 1 1
      1 0 0 0 0 0 0 0 0
      0 a -a 0 0 b 0 0 0
      0 0 -c 0 0 0 e 0 0
      0 0 0 -f 0 0 0 g 0
      0 -h 0 h 0 0 0 0 n];
      x1=V[5,i]-currentind[1,i-1]; x2=currentind[1,i-1]-V[6,i]+V[9,i]; x3=V[6,i]-currentcap[1,i-1]+V[7,i]; x4=currentcap[1,i]-V[8,i]-V[9,i] ;
      A =[x1
          x2
          x3
          x4
          vp*sin.(2*π*freq.*t'[1,i])
          0
          0
          0
          0];
        x=Y\A;
        V[:,i]=x;
        currentcap[1,i]=(C/dt)*(V[3,i]-V[3,i-1]-V[4,i]+V[4,i-1]);
         voltagecap[1,i]=V[3,i]-V[4,i];
        currentind[1,i]=(dt/L)*(V[1,i]-V[2,i]+V[1,i-1]-V[2,i-1])+currentind[1,i-1];
        if V[2,i]-V[3,i]>0 || V[6,i]>0
           a=1;b=0;
        elseif V[6,i]<=0
             a=0; b=1;
        else
          a=0; b=1;
        end

        if -V[3,i]>0 || V[7,i]>0
           c=1; e=0;
        elseif V[7,i]<=0
             c=0; e=1
        else
            c=0; e=1;
        end
       if V[4,i]>0 || V[8,i]>0
          f=1; g=0;
       elseif V[8,i]<=0
          f=0; g=1
       else
          f=0; g=1;
       end
       
       if V[4,i]-V[2,i]>0 || V[9,i]>0
          h=1; n=0;
       elseif V[9,i]<=0
          h=0; n=1
       else
          h=0; n=1;
       end
end

voltagecap=voltagecap';
plot(t,voltagecap)

```

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