Problem with vpa integral
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Aviral Srivastava
on 15 Mar 2024
Commented: Walter Roberson
on 15 Mar 2024
Vu(k,T) = ((gama_q.*(g2).*(T^2)))./(2*k);
Vii_u(k,T) = diff(Vu ,k );
rho_u(k,T) = (-Vii_u).*(Vu^2)*l1;
%Fi_u = matlabFunction(rho_u.*l1);
Fii( 1 ) = vpaintegral(rho_u, k_min_q ,4*k_min_q);
P.S. I am using vpaintegral becasue int does not yield a functional expression and fails to calculate integral. I tried numerical approach but the error is above the bounds. Once I get Fii as a function of T then I need to differenciate Fii w.r.t T.
k and T are sym variables;
g2 is another sym expression of the following form
g2(k) = N./log(1 + ((k.^2)./lambda^2));
I want Fii(1) to be an integrak done w.r.t k so that the resultant expression is a function of only T.
I am getting the follwing error:
The following error occurred converting from symfun to double:
Unable to convert expression into double array.
Error in m_t_u_B2_transition (line 61)
Fii( 1 ) = vpaintegral(rho_u, k_min_q ,4*k_min_q);
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Accepted Answer
Steven Lord
on 15 Mar 2024
This type of error indicates you're assiging a symbolic expression into an element of a double array. When you do this, MATLAB will attempt to convert the symbolic expression into double so it "fits" in the double array. Sometimes this works.
sqrt2 = sqrt(sym(2))
doubleArray = zeros(1, 5)
doubleArray(2) = sqrt2
Sometimes MATLAB cannot perform that conversion.
syms x
symArray = zeros(1, 5, 'sym')
symArray(2) = sqrt2
symArray(4) = x^2
doubleArray(4) = x^2
Two potential ways to resolve this error could be to substitute numeric values into the symbolic expression, so instead of a value like "x^2" it has a numeric value (if I substituted x = 3 into the symbolic expression x^2, MATLAB would store the value 9 in doubleArray(4)) or to define the array as symbolic at the start rather than double (like I did with symArray above.)
5 Comments
Torsten
on 15 Mar 2024
We might be able to help if you supply executable code that reproduces the error message you get. The code from above is incomplete because sym declarations and/or parameters are missing.
Walter Roberson
on 15 Mar 2024
Fii( 1 ) = vpaintegral(rho_u, k_min_q ,4*k_min_q);
You must have previously assigned Fii as a numeric array. You need to insert
Fii = sym(Fii);
before the above statement to fix this problem.
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