Rearrange Variables in an equation that are changing everytime

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I want to get one variable in terms of the other variables in the equation. For example
syms a b
eqn = ('a + 2*b = 1')
v_a = solve(eqn, a)
v_b = solve(eqn, b)
This works fine
My issue is that the variables and the number of variables can change in each iteration.
My variables alpha1, alpha2 and alpha3 are defined by sym and not syms. I need to do this as the no of alpha's is determined by the input data size. This case 3.
data = [-1 0 1;-1 +1 -1]';
alpha = sym('alpha',[1 3]); %output "[ alpha1, alpha2, alpha3]"
st = 'alpha*data(:,2)=0' %output should be "alpha2 - alpha1 - alpha3 = 0" but I dont get this. instead, its something else
v_2 = solve(st,alpha(1)) %doesnt work because the previous line is wrong
Thanks and appreciate any help

Accepted Answer

Star Strider
Star Strider on 20 Jul 2012
data = [-1 0 1;-1 +1 -1]';
alpha = sym('alpha',[1 3]);
advct = alpha * data(:,2)
v_2 = solve(advct == 0, alpha(1))
gives me these:
advct =
alpha2 - alpha1 - alpha3
v_2 =
alpha2 - alpha3
Is that the result you were hoping for?
Mech Princess
Mech Princess on 21 Jul 2012
Edited: Mech Princess on 21 Jul 2012
Thanks Walter Roberson. I cannot see your editing though.
Removed single quotes. still gave same error. Following worked. I removed "st==0" and just gave "st" and it worked.
data = [-1 0 1;-1 +1 -1]'; alphavec = sym('alpha',[1 3]); st = alphavec*data(:,2); v_2 = solve(st,alpha(1));
Thanks so much again. I have just finished step 5 of 10 to finish the code and I am bound to run into more code challenges in future.
Thank you so much Star Strider. Thanks so much both of you as I learnt so much more than just the code
Star Strider
Star Strider on 21 Jul 2012
My pleasure! We are here to help.
And thank you again for accepting my answer!

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