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sum calculation in matlab

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MariapL
MariapL 2017-11-19
评论： Star Strider 2017-11-21
Hi, I have problem starting calculation of this sum
SUM(ZnSn-aSnSn+bSnTn)=0
Sum(ZnTn-aSnTn+bTnTn)=0
So I have S1 S2 S3 Z1 Z2 Z3 T1 T2 T3
I need to calculate a and b. I kinda can do it on paper by the point is to see how matlab calculate it. It should go like
Z1S1-aS1S1+bS1T1 + Z2S2-aS2S2+bS2T2 + Z3S3-aS3S3+b32T3=0
Z1T1-aS1T1+bT1T1 + Z1T1-aS1T1+bT1T1 +Z1T1-aS1T1+bT1T1 =0
How should I start it, I m super new at matlab. Should I use sum , and set a and b as vector of 0 ? Any help much appreciated

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回答（2 个）

Star Strider
Star Strider 2017-11-19
Note that ‘32T3’ is not a valid MATLAB variable name (they cannot begin with numbers). I changed it to ‘S2T3’, and used the Symbolic Math Toolbox:
syms a b Z1S1 S1S1 S1T1 Z2S2 S2S2 S2T2 Z3S3 S3S3 S2T3 Z1T1 T1T1
Eqns = [Z1S1-a*S1S1+b*S1T1 + Z2S2-a*S2S2+b*S2T2 + Z3S3-a*S3S3+b*S2T3 == ...
Z1T1-a*S1T1+b*T1T1 + Z1T1-a*S1T1+b*T1T1 +Z1T1-a*S1T1+b*T1T1];
[a,b] = solve(Eqns, [a b])
to produce:
a =
(S1T1*Z1T1 + S2T2*Z1T1 + S2T3*Z1T1 - T1T1*Z1S1 - T1T1*Z2S2 - T1T1*Z3S3)/(S1T1*S2T2 + S1T1*S2T3 - S1S1*T1T1 - S2S2*T1T1 - S3S3*T1T1 + S1T1^2)
b =
(S1S1*Z1T1 - S1T1*Z1S1 + S2S2*Z1T1 - S1T1*Z2S2 + S3S3*Z1T1 - S1T1*Z3S3)/(S1T1*S2T2 + S1T1*S2T3 - S1S1*T1T1 - S2S2*T1T1 - S3S3*T1T1 + S1T1^2)
I have no idea if these will produce usable results, since I do not know what any of the variables are (scalars, matrices, ...).
  2 个评论
MariapL
MariapL 2017-11-21
Is there any way to not include 'syms'? I have tried to intall it couple of time but still got an error. Thanks:)
Star Strider
Star Strider 2017-11-21
You do not need to use the Symbolic Math Toolbox. I used it to solve for ‘a’ and ‘b’, so all you need to do is to use the equations I provided, with your numeric variables, to find the parameter values.

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Torsten
Torsten 2017-11-21
If you define Z, S, T as numerical arrays, you can determine a and b as
A = [-sum(S.*S) sum(S.*T);-sum(S.*T) sum(T.*T)];
rhs = [-sum(Z.*S);-sum(Z.*T)];
x = A\rhs;
a = x(1);
b = x(2);
a
b
Best wishes
Torsten.

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