Using vpasolve to solve equation for all values in matrix

Question

Maria 2018-6-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/403886-using-vpasolve-to-solve-equation-for-all-values-in-matrix

评论： Maria 2018-6-5

Is it possible to use vpasolve to solve a particular equation for all values in a matrix without looping? i have a large number of matrices and looping through them all will be very slow.

% Minimal working example
    h=rand(5,5);
    h_long=reshape(h,[size(h,1)*size(h,2),1]);
    store_arr=zeros(numel(h_long),1);
    for a=1:numel(h_long)
        curr_pix=h_long(a);
         tt=vpasolve(5*((1-exp(-5/x)*sind(14))/((1-exp(-5/x))*cosd(14)))==curr_pix, x);
         store_arr(a)=tt;
    end
    fin_mat=reshape(squeeze(store_arr),size(h))

This is a miniature version of what i am doing. my matrix has 4 dimensions and are quite large.

Thanks,

Maria

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 2018-6-4

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/403886-using-vpasolve-to-solve-equation-for-all-values-in-matrix#answer_323086

在 MATLAB Online 中打开

No, vpasolve() will always consider matrix inputs as being equations to be solved simultaneously.

If you switch to symbolic curr_pix then you can solve() the equation, getting

ttsol = -5./ln(-(-5+curr_pix*cosd(14))./(-curr_pix*cosd(14)+5*sind(14)))

after which you can fin_mat = subs(ttsol, curr_pix, h) to get a matrix of solutions that skips the reshapes()

3 个评论
显示 1更早的评论隐藏 1更早的评论

Walter Roberson 2018-6-4

在 MATLAB Online 中打开

As long as you have the values of h, then what I showed should work.

h = ... whatever
syms curr_pix x
angd = sym(14);
ttsol = simplify( solve(5*((1-exp(-5/x)*sind(angd))/((1-exp(-5/x))*cosd(angd)))==curr_pix, x) );
fin_mat = subs(ttsol, curr_pix, h);