Missing coefficients in symbolic expressions with coeffs

Ok, I have been trying to use coeffs here is what I am currently have a problem with, although I have 5 symbolic variables, not all show up in every equation so when I try and gather coeffients I would like to be able to catch even the 0 values. heres what I have so far.

clc
clear 
m= [2 -3 ; 3 -2];
q = [ -1 -1]';
xv = sym('x1');
lm = length(m);
yv = sym(zeros(1, lm))';
zv = sym(zeros(1, lm))';
for k=1:lm
yv(k) = sym(sprintf('x%d', k+1));
zv(k) = sym(sprintf('x%d', k+lm+1));
end
A = [-(m*yv+xv*q);m*yv+xv*q-zv; yv-zv;zv-yv];
Aineq=zeros;
temp = zeros;
for i=1:length(A)
  temp=coeffs(A(i,:))
  for j=1:length(temp)
      Aineq(i,j)=temp(j)
  end
end
Aineq

the last nested for was my attempt to gather the coefficients. I but I cannot place them in the right way this way. Any suggestions? I have looked at ineval and feval but I do not see the how to use these tools

Oh this is what my output looks like A =

   -2*x2+3*x3+x1
   -3*x2+2*x3+x1
 2*x2-3*x3-x1-x4
 3*x2-2*x3-x1-x5
           x2-x4
           x3-x5
           x4-x2
           x5-x3  
  Aineq =

     1    -2     3     0
     1    -3     2     0
    -1     2    -3    -1
    -1     3    -2    -1
     1    -1     0     0
     1    -1     0     0
    -1     1     0     0
    -1     1     0     0  
So this is where I am stuck at this point.

[Mech Princess]

Hi. does any one know how to do this when the expressions in A has constants also? I tried the code and it gets errors because of the constants. Thanks

Answer 1

[Nick Drake]

This is what I was able to do thanks for all the help. I will post the final solution to the larger problem if anyone wants to see it.

    clc
    clear 
    m= [2 -3 ; 3 -2];
    q = [ -1 -1 ]';
    xv = sym('x1');
    lm = length(m);
    yv = sym(zeros(1, lm))';
    zv = sym(zeros(1, lm))';
    for k=1:lm
    yv(k) = sym(sprintf('x%d', k+1));
    zv(k) = sym(sprintf('x%d', k+lm+1));
    end
    A = [m*yv+xv*q+zv;-(m*yv+xv*q); yv-zv;zv-yv];
    for i=1:length(A)
        A(i,:)=sort(A(i,:));
    end
    xx = cat(1,xv ,yv,zv);
    Aineq = zeros(numel(A),numel(xx));
    for j=1:length(A)
        for i=1:length(xx)
        y=xx(i);
        [c,t]=coeffs(A(j),y);
            if (length(t)<2)
            else
                insert=c(2);
                Aineq(j,i)=insert;
            end
        end
    end
    Aineq;
    bineq=zeros(length(Aineq),1);
    for temp=1:(length(zv))
            bineq(temp,1)=1;
    end

[Mech Princess]

There is an error in the if-else statement: Anyone has a solution? Thanks

    ??? The following error occurred converting from sym to double:
    Error using ==> mupadmex
    Error in MuPAD command: DOUBLE cannot convert the input expression into a double array.

If the input expression contains a symbolic variable, use the VPA function instead.

Answer 2

[Andrei Bobrov]

xx = symvar(A);
Aineq = zeros(numel(A),numel(xx));
for j1 = 1:numel(A)
    [v1,v2] = coeffs(A(j1),xx);
    Aineq(j1,ismember(xx,v2)) = v1;
end

on Nick Drake comment: try code

xx = cat(1,xv ,yv,zv)
Aineq = zeros(numel(A),numel(xx));
for j1 = 1:numel(A)
    [v1,v2] = coeffs(A(j1),xx);
    Aineq(j1,ismember(xx,v2)) = v1;
end

on Nick Drake comment2, on PC (W7 32 bit, MATLAB R2011b):

[Nick Drake]

Could you possibly explain this a little to me I am getting an error when trying to run the code

??? Error using ==> sym.eq at 20

Array dimensions must agree.

Error in ==> symvar at 27

[b,e] = findrun(s==' ');

[Nick Drake]

I am still receiving an error when I ran this part of the code

>> xx = cat(1,xv ,yv,zv)

Aineq = zeros(numel(A),numel(xx));

for j1 = 1:numel(A)

[v1,v2] = coeffs(A(j1),xx);

Aineq(j1,ismember(xx,v2)) = v1;

end

xx =

x1

x2

x3

x4

x5

??? The following error occurred converting from sym to double:

Error using ==> sym.double at 25

DOUBLE cannot convert the input expression into a double array.

If the input expression contains a symbolic variable, use the VPA function instead.

>> whos

Name Size Bytes Class Attributes

A 8x1 700 sym

Aineq 8x5 320 double

i 1x1 8 double

j1 1x1 8 double

k 1x1 8 double

lm 1x1 8 double

m 2x2 32 double

q 2x1 16 double

v1 1x1 148 sym

v2 1x1 126 sym

xv 1x1 128 sym

xx 5x1 384 sym

yv 2x1 192 sym

zv 2x1 192 sym