A matrix with class of sym, but symvar() command gives empty results

Question

Muzaffer Citir 2019-12-30

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/498414-a-matrix-with-class-of-sym-but-symvar-command-gives-empty-results

评论： Muzaffer Citir 2020-1-2

I have a huge matrix with more than 180 different symbolic variable. I need to change variables into vector form such from q1, q2 ... to q(1), q(2)...

I wrote a code as below, I succided to change variable. But problem, now I lost my symbolic variables, when I query my variables with symvar(), I get empty results.

This is problem when I try to change from symbolic to function with matlabFunction() command. Naturally, it can not find any variable in my symbolic func.

Please help me

That is the result wtih symvar():

>> symvar(tests.test5.symbolicObsW{3,1})

ans =

Empty sym: 1-by-0

That is result with matlabFunction():

>> testRecords.funcObsw3 = matlabFunction(tests.test5.symbolicObsW{3,1});

Warning: Function 'sq' not verified to be a valid MATLAB function.

for cJ=1:6
    tic;
    for t=NumRow 
     ObsWsym{cJ,:}(t,:) = subs(regressors{cJ,1}(1,:), [q1, q2, q3, q4, q5, q6,...
             dq1, dq2, dq3, dq4, dq5, dq6,...
             ddq1, ddq2, ddq3, ddq4, ddq5, ddq6],...
             [sq(18*t-18+1), sq(18*t-18+2), sq(18*t-18+3),sq(18*t-18+4),sq(18*t-18+5),sq(18*t-18+6),...
             sq(18*t-18+7), sq(18*t-18+8), sq(18*t-18+9),sq(18*t-18+10),sq(18*t-18+11),sq(18*t-18+12),...
             sq(18*t-18+13), sq(18*t-18+14), sq(18*t-18+15),sq(18*t-18+16),sq(18*t-18+17),sq(18*t-18+18)]); %#ok<AGROW>
    end
    disp(['Observation matrix (',...
        num2str(size(ObsWsym{cJ,1},1)),...
        'X',num2str(size(ObsWsym{cJ,1},2))...
        ') for Joint ',num2str(cJ),' is generated by using Regressor']);
    toc;
end 

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2019-12-30

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/498414-a-matrix-with-class-of-sym-but-symvar-command-gives-empty-results#answer_408096

在 MATLAB Online 中打开

You should probably just use matlabFunction with the 'vars' option. Pass in a cell array. Within the cell array, each variable that is listed in the same entry will be bundled into a single parameter. So for example if you had

q = symvar('q', [1 150]);
p = symvar('p', [1 30]);
testRecords.funcObsw3 = matlabFunction(tests.test5.symbolicObsW{3,1}, 'vars', {q, p})

then the function would be created with two parameters, one of which was expected to be a row vector of length 150, and the other was expected to be a row vector of length 30.

Warning: Function 'sq' not verified to be a valid MATLAB function.

You appear to be trying to mix array indexing with symbolic work. That will fail most of the time: never try to index with a symbolic variable (unless you really really know what you are doing.)