Matlab symbolic : calculate expression with vector of symbolic variables - MATLAB Answers

Hello,

I need to calculate with Matlab symbolic the following expression :

"l" is a vector of symbolic variables and "C_l" also (same length than "l", that is to say, `l_max -l_min = 3000-10=2990`).

To calculate this, I did :

       
         clear
        
         syms
        
         l_min l_max fsky Np var1D varO1
        
         l_min = 10
        
         l_max = 3000
        
         l = sym(
        
         'l_'
        
         ,[1 (l_max - l_min)])
        
         C_l = sym(
        
         'C_l_'
        
         ,[1 (l_max -l_min)])
        
         % First observable
        
         var1D = symsum(2/((2*l+1)*fsky*Np^2), l, l_min, l_max)
        
         varO1 = var1D/symsum(C_l, l_min, l_max)^2

Error using symengine

Invalid operands.

Error in sym/privBinaryOp (line 1030)

Csym = mupadmex(op,args{1}.s, args{2}.s, varargin{:});

Error in / (line 373)

X = privBinaryOp(A, B, 'symobj::mrdivide');

Error in inequality (line 9)

var1D = symsum(2/((2*l+1)*fsky*Np^2), l, l_min, l_max)

I don't know to proceed to compute the expression of sigma_o,1^2 just above (varO1 in the code snippet).

Where is my error ?

https://www.mathworks.com/matlabcentral/answers/1607075-matlab-symbolic-calculate-expression-with-vector-of-symbolic-variables#answer_1355727

Use the element wise operator for / and ^ ... i.e. ./ and .^ as below

clear

syms l_min l_max fsky Np var1D var2D varO1 varO2

l_min = 10

l_max = 300

syms L

%l = sym('l_',[1 (l_max - l_min)])

C_l = sym( 'C_l_' ,[1 (l_max -l_min)])

C_l =

% First observable

var1D = symsum(2/((2*L+1)*fsky*Np^2), L, l_min, l_max)

var1D =

varO1 = var1D/sum(C_l)^2

varO1 =

% Second observable

var2D = symsum(((2*L+1)*fsky*Np^2), L, l_min, l_max)

var2D =

varO2 = var2D./symsum((2*L+1)*C_l, L, l_min, l_max).^2 % use element wise operator

varO2 =

https://www.mathworks.com/matlabcentral/answers/1607075-matlab-symbolic-calculate-expression-with-vector-of-symbolic-variables#answer_851645

have done some progress in investigation to compute the 2 variances :

Now, I did :

                            
                              clear
                             
                              syms
                             
                              l_min l_max fsky Np var1D var2D varO1 varO2
                             
                              l_min = 10
                             
                              l_max = 3000
                             
                              syms
                             
                              l
                             
                              %l = sym('l_',[1 (l_max - l_min)])
                             
                              C_l = sym(
                             
                              'C_l_'
                             
                              ,[1 (l_max -l_min)])
                             
                              % First observable
                             
                              var1D = symsum(2/((2*l+1)*fsky*Np^2), l, l_min, l_max)
                             
                              varO1 = var1D/sum(C_l)^2
                             
                              % Second observable
                             
                              var2D = symsum(((2*l+1)*fsky*Np^2), l, l_min, l_max)
                             
                              varO2 = var2D/symsum((2*l+1)*C_l, l, l_min, l_max)^2

But I still get an error at the last line :

                            
                              var2D =
                             
                              9005901*Np^2*fsky
                             
                              Error
                             
                              using symengine
                             
                              Not
                             
                              a square matrix.
                             
                              Error
                             
                              in sym/privBinaryOp (line 1030)
                             
                              Csym = mupadmex(op,args{1}.s, args{2}.s, varargin{:});
                             
                              Error
                             
                              in ^ (line 330)
                             
                              B = privBinaryOp(A, p,
                             
                              'symobj::mpower'
                             
                              );
                             
                              Error
                             
                              in inequality (line 15)
                             
                              varO2 = var2D/symsum((2*l+1)*C_l, l, l_min, l_max)^2

The issue is that I don't know how to mix the classical "`sum`" function and the "`symsum`" symbolic function because I have the following expression in divider :

varO2 = var2D/symsum((2*l+1)*C_l, l, l_min, l_max)^2

Anyone could see a workaround ?

https://www.mathworks.com/matlabcentral/answers/1607075-matlab-symbolic-calculate-expression-with-vector-of-symbolic-variables#comment_1890460

https://www.mathworks.com/matlabcentral/answers/1607075-matlab-symbolic-calculate-expression-with-vector-of-symbolic-variables#comment_2966817

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!