increase accuracy and decrease numerical problems with "roots" function in matlab function block in Simulink

Hello matlab and Simulink community,

i doing a project in simulik, in the project i need to solve quartic equation a*x^4+b*x^3+c*x^2+d*x+e=0 when a,b,c,d,e are real numbers that change in time a(t),b(t),c(t),d(t),e(t), so i need to solve quartic equation many times.

in order to solve the quartic equation i use "roots" in a matlab function block in simulink.

the code in the matlab function block is:

#start

function [r] = fcn(a,b,c,d,e)

p = [a b c d e];

r = roots(p)

#finish

i want to increase accuracy and decrease numerical problems in order to get the roots of the eqation as percise as possible, and also with more digits of percision.

i try to use "vpa" with "roots" but it does not work.

i would like to get some help =)

Answer 1

[Keshav]

Hi Ram,

I understand that you are using MATLAB “roots” function to find the root of a polynomial equation. And you want to increase the accuracy and precision of the root. Please try to use MATLAB “vpasolve” function to find the root of polynomial equation.

You can find the MATLAB documentation for “vpasolve” function on the below link: https://www.mathworks.com/help/symbolic/sym.vpasolve.html?s_tid=srchtitle_vpasolve_1

Example of vpasolve (Let’s suppose you want to find the root of equation x^2 + 2*x + 3 = 0 with 40 digit precision)

syms x
digits(40)
vpasolve(x^2 + 2*x + 3 == 0,x);