## Order of variables in SOLVE

on 14 May 2013

### Walter Roberson (view profile)

```clear all
syms x y l1 l2 l3   %%Generate symb var for multipliers
v=[x y l1 l2 l3];
g2=(x-2)/sqrt((x-2)^2+(y-3)^2)+l1;
```
```cs1=l1(x+y);  %% Complementary slackness conditions
cs2=l2*(x-2);
cs3=l3*(x+2);
```
```[x, y, l1, l2, l3] = solve(g1==0,g2==0,cs1==0,cs2==0,cs3==0, x, y, l1,...
l2, l3);
sol=[x, y, l1, l2, l3];
```

I have this KKT system. Other times when I used the solve command I noticed that in the solution matrix the variables are not reported in the specified order.

How do I make sure that in the sol matrix the variable are the right one (without checking manually, that is).

In the example above, having the solutions, I can see that into sol x,y are the two rightmost columns. If I switch like this

```[ l1, l2, l3, *x, y,*] = solve(g1==0,g2==0,cs1==0,cs2==0,cs3==0, x, y, l1,...
l2, l3);
```

then everything goes ok. I need to now why this happens in order not to make this mistake again when I don't have solutions. Thanks

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### Walter Roberson (view profile)

on 14 May 2013

Use the structure return form of solve and then extract by structure field name into the variables you want.

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