# FSOLVE requires all values returned by functions to be of data type double. showing while solving an algebraic equation in matlab ??

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Surendra Ratnu on 8 Dec 2023
Commented: Dyuman Joshi on 5 Feb 2024 at 11:36
I want to solve the eqs for u_s and find out the value of u_s but i am getting error while solving the equation using fsolve. Can you provide some solution for this problem ?? Thank you
type untitled03.m
clc clear close all a = deg2rad(45); m = 0.683; We = 277; Re = 75; b = (-0.13*m.^3+0.263*m.^2 +0.039*m +0.330)/tan(a); s_b = 0.0042; p = pi/2; R = 1.7440; t = deg2rad(0); syms q x = b*cos(t)*sin(a)^2; x01 = 4*((1-cos(t)^2*cos(a)^2)); x02 = (b*sin(t)*sin(a))^2; q_j = -((x -(x01-x02)^0.5)/(x01/4)); d = (b^2*sin(a)^2 + q^2*(1-cos(t)^2*cos(a)^2) + 2*b*q*cos(t)*sin(a)^2)^0.5; u_j = 2*(m-1)*(4*d^2-1) + m; F = int(q*u_j, q, 0, q_j); G = int(q*u_j^3,q,0,q_j); eqs = @(u_s)((4*sin(a).^3*F.^4*(R-q_j)*(R.^5-q_j.^5))/(15*q_j.^7*R.^5*Re))+... ((((R.^3-q_j.^3)*F.^3*sin(a).^3)/(9*q_j.^3*R.^3))-((R-q_j)*F*((4/q_j)+sin(a))))*u_s+... (R-q_j)*F*sin(a)*u_s.^3+... (R.^2 +2*R*sqrt(pi*s_b))+(16*F.^3*sin(a)*(R-q_j).^2)/(3*q_j.^3*R*Re)*u_s^2; sol = fsolve(eqs,0.5);

Walter Roberson on 8 Dec 2023
F and G are int() calls. Even if they evaluate to closed forms that were rational numbers, they have symbolic results. When you create an anonymous function that includes F and G, any numeric coefficients will be converted to symbolic at the point F or G is encountered, so the anonymous function will return something of data type sym even in the best possible case. But fsolve requires single or double. fsolve refuses to even try to convert sym to double.
Instead of constructing that anonymous function you should use matlabFunction()
Surendra Ratnu on 8 Dec 2023
It works. Thank you for your suggestions
Dyuman Joshi on 5 Feb 2024 at 11:36

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