problems about solve exponential function
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Hi,
please have a look at a part of my code in the function maxmin0. The general idea is that I use solve to get the solution for a exponential function funcion, and then assign the solution to a variable called pf5, which is the output for maxmin0. The function runs well itself. But when I call this function in another function, it always show a error message . I am doubting it is the way I write the this function is not smart and so there is problem when it is being called...Could you help to check that?
Here is the code
if true
% p1=1-lb2-lb3;
p2=lb2;
p3=lb3;
if (d2(i,3)==d2(i,1))
pf5(2,i)=[0;0];
eu(i)=-Inf;
else
coef1=d1(i,1)+(d1(i,1)-d1(i,3))*d2(i,1)/(d2(i,3)-d2(i,1));
coef2=d1(i,2)+(d1(i,1)-d1(i,3))*d2(i,2)/(d2(i,3)-d2(i,1));
coef3=d1(i,3)+(d1(i,1)-d1(i,3))*d2(i,3)/(d2(i,3)-d2(i,1));
syms x
f5=simplify(p1*coef1*exp(-r*coef1*x)+p2*coef2*exp(-r*coef2*x)+p3*coef3*exp(-r*coef3*x));
y5(i)=solve(f5,x);
pf5(1,i)=double(y5(i));
end
and here is the error message
Warning: Explicit solution could not be found.
> In solve at 169
In maxmin0 at 138
In maxmin at 15
In beta at 18
In C:\Program Files\MATLAB\R2012a\toolbox\shared\optimlib\finDiffEvalAndChkErr.p>finDiffEvalAndChkErr at 26
In C:\Program Files\MATLAB\R2012a\toolbox\shared\optimlib\finitedifferences.p>finitedifferences at 128
In C:\Program Files\MATLAB\R2012a\toolbox\optim\optim\private\computeFinDiffGradAndJac.p>computeFinDiffGradAndJac at 28
In C:\Program Files\MATLAB\R2012a\toolbox\optim\optim\barrier.p>barrier at 135
In fmincon at 841
In main at 6
Error using mupadmex
Error in MuPAD command: Subscripted assignment dimension mismatch
Error in sym/subsasgn (line 1638)
C = mupadmex('symobj::subsasgn',A.s,B.s,inds{:});
Error in maxmin0 (line 138)
y5(i)=solve(f5,x);
Error in maxmin (line 15)
[PF0,eu0]=maxmin0(sub,DD);
Error in beta (line 18)
mu = maxmin(sub,DD);
Error in C:\Program Files\MATLAB\R2012a\toolbox\shared\optimlib\finDiffEvalAndChkErr.p>finDiffEvalAndChkErr (line 26)
Error in C:\Program Files\MATLAB\R2012a\toolbox\shared\optimlib\finitedifferences.p>finitedifferences (line 128)
Error in C:\Program Files\MATLAB\R2012a\toolbox\optim\optim\private\computeFinDiffGradAndJac.p>computeFinDiffGradAndJac (line 28)
Error in C:\Program Files\MATLAB\R2012a\toolbox\optim\optim\barrier.p>barrier (line 135)
Error in fmincon (line 841)
[X,FVAL,EXITFLAG,OUTPUT,LAMBDA,GRAD,HESSIAN] = barrier(funfcn,X,A,B,Aeq,Beq,l,u,confcn,options.HessFcn, ...
Error in main (line 6)
[x,fval,exitflag,output,lambda,grad] = fmincon(@beta,[0.2,0.2,0.2,0.01,20,0.1,20,0.1],A,b,[],[],lb,ub,[],options)
4 个评论
Walter Roberson
2013-2-15
At the point of the solve(), could you show us what f5 is? I want to check for solutions myself.
xueqi
2013-2-16
TUHAME STEVEN
2015-10-28
it is fine thank you
采纳的回答
Carlos
2013-2-14
编辑：Walter Roberson
2013-2-14
When you execute this code in Matlab
>> syms x;
>> f=-10*exp(-x);
>> solve(f,x)
>> isempty(a)
ans =
1
Whereas if you execute this code
>> syms x;
>> f=x^2-4
>> solve(f,x)
>> isempty(a)
ans =
0
You can use the isempty command. If isempty returns true (1), it means your roots array is empty because there are no roots.
更多回答（1 个）
Carlos
2013-2-13
编辑：Walter Roberson
2013-2-14
In the warning message displayed by Matlab it says no solution has been found(just as it happens if the function has no roots), and exp(-ax) has no roots, this is what happens when I try the following code in Matlab
>> syms x;
>> f=-10*exp(-x);
>> solve(f,x)
Warning: Explicit solution could not be found.
> In solve at 81
ans =
[ empty sym ]
However if there is no problem with Matlab 2010 this might not be the case, I just wanted you to consider the possibility the function has no roots.
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