Error using sym/subsref
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I have this program to get the value of "m"
clc
syms m
eqns = (72*m^2)-(1.5*m^3) == 358;
S=solve (eqns,m,'Real',true)
double (S.m);
However in the output I get this error
S =
32*cos(atan(2167511^(1/2)/5965)/3) + 16
16*3^(1/2)*sin(atan(2167511^(1/2)/5965)/3) - 16*cos(atan(2167511^(1/2)/5965)/3) + 16
16 - 16*3^(1/2)*sin(atan(2167511^(1/2)/5965)/3) - 16*cos(atan(2167511^(1/2)/5965)/3)
Error using sym/subsref
Too many output arguments.
Error in Untitled (line 5)
double (S.m);
Can any body help me with this?
采纳的回答
Walter Roberson
2020-5-4
When there is only a single variable being solved for, and ReturnConditions is not set, then solve() does not return a structure containing the one variable: it returns the value of the variable. In terms of your code, that means you would use
double(S) %instead of double(S.m)
Or you could instead
S=solve (eqns, m, 'Real', true, 'returnconditions', true);
and then S.m would exist.
更多回答（1 个）
Mathias Andersen
2020-5-4
1 个投票
Double(S) will produce a matrix with the solutions.
S.m is not a variable stated anywhere in the script
4 个评论
Rohit Tamrakar
2020-5-4
Walter Roberson
2020-5-4
S is the output of solve(). If two or more variables were being solved for and a single output were given, then S would be a structure with one field for each variable being solved for, and then S.m would exist.
S.m would also be created if 'returnconditions', true is specified.
Mathias Andersen
2020-5-4
编辑：Mathias Andersen
2020-5-4
S contains the values for m
Walter Roberson
2020-5-4
Not when you solve for a single variable and you do not have ReturnConditions true: in that case, MATLAB cannot tell that apart from the case where you want the non-struct version of the solution.
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