Index exceeds the number of array elements (1).

When I want to run and plot the quadratic solver, I met the error 'Index exceeds the number of array elements (1)'.

% Some code to show you how to handle arithmatic involving complex numbers
clc
clear
% We'll write some code that solves a simple quadratic equation.
% The roots of the quadratic can either be real or complex and this depends
% upon the coefficients in a the original equation.
%
% Equation has the form:
% ax^2+bx+c=0
%
% Coefficient 'c' varied in magnitude so that a mix of real and complex
% roots are generated.  Top tip - the above equation could be the characteristic
% equation of the car and 'c' could be vehicle speed.
%
% Initialise the variables that define the roots of our quadratic (defined
% as complex numbers)
x1com=complex(0.0,0.0);
x2com=complex(0.0,0.0);
%
M_ul = 1995; Md = 60; I = 3877;
M = M_ul + Md;
l_f = 1.34; l_r = 1.12;l_wb = 2.46; Rmean = 60; t = 1.62;
K_f = 55000; K_r = 65000;u=1;
% Specify the values of the coefficients of the quadratic
a=1;
b=(2*M*(l_f^2*K_f+l_r^2*K_r)+2*I*(K_f+K_r))/M*u*I;
c=((4*K_f*K_r*l_wb^2)/(M*I*u^2))-(2*(l_f*K_f-l_r*K_r)/I);
%
for u=1:50
    c=c(1+u);
    b=b(u+1);
    x1com=(-b+sqrt(b^2-4*a.*c))/(2*a);
    x2com=(-b-sqrt(b^2-4*a.*c))/(2*a);
% Extract the real and imaginary parts from the roots of the quadratic 
% (which have been calculated as complex numbers)
% Place these into real vectors
    x1real(u)=real(x1com);
    x1imag(u)=imag(x1com);
    x2real(u)=real(x2com);
    x2imag(u)=imag(x2com);
end
%
% Generate some graphs to illustrate results using the real vectors
% 1) Re vs Im
subplot(3,1,1)
plot(x1real(:),x1imag(:),'ko',x2real(:),x2imag(:),'b+')
% axis([xmin xmax ymin ymax]) % Use this to define axis limits
legend('Root 1','Root 2','Location','EastOutside')
title('Roots of quadratic equation');
grid on
xlabel('Real')
ylabel('Imaginary')
% 2) Re vs c
subplot(3,1,2)
plot(c(:),x1real(:),'ko',c(:),x2real(:),'b+')
% axis([xmin xmax ymin ymax]) % Use this to define axis limits
legend('Root 1','Root 2','Location','EastOutside')
grid on
xlabel('Coefficient c')
ylabel('Real')
% 3) Im vs c
subplot(3,1,3)
plot(c(:),x1imag(:),'ko',c(:),x2imag(:),'b+')
% axis([xmin xmax ymin ymax]) % Use this to define axis limits
legend('Root 1','Root 2','Location','EastOutside')
grid on
xlabel('Coefficient c')
ylabel('Imaginary')
%
% Save the graph as a .jpg and place in working directory
saveas(gcf,'examplegraph.jpg','jpg');

[Dennis]

You try to access b(u+1) and c(u+1) in these lines:

    c=c(1+u);
    b=b(u+1);

but b and c only have 1 entry.

[Yixuan LU]

could you please tell me how to fix it to run the loop? Thanks

[Dennis]

I am not sure what you are trying to do.

Removing those two lines would 'fix' your code, as they are not only causing an error, but also have no effect.

Are there supposed to be more values stored in b or c?

[Yixuan LU]

b and c are the variables against u and what I want is to get matrix of b and c when u increaseing so that I can get a series of results for the quadratic equation

[Dennis]

You only calculate the values of b and c for u=1. Maybe you want to change

%u=1;
u=1:50;

and

 %   c=c(1+u);
 %   b=b(u+1);
  %  x1com=(-b+sqrt(b^2-4*a.*c))/(2*a);
  %  x2com=(-b-sqrt(b^2-4*a.*c))/(2*a);
  x1com=(-b(u)+sqrt(b(u)^2-4*a.*c(u)))/(2*a);
  x2com=(-b(u)-sqrt(b(u)^2-4*a.*c(u)))/(2*a);

Answer 1

[Krishna Zanwar]

In the code above 'b' and 'c' are scalars and cannot be indexed. If you want to get an array of 'b' and 'c' as 'u' is increasing you sould put them inside the for loop.

b(u)=(2*M*(l_f^2*K_f+l_r^2*K_r)+2*I*(K_f+K_r))/M*u*I;
c(u)=((4*K_f*K_r*l_wb^2)/(M*I*u^2))-(2*(l_f*K_f-l_r*K_r)/I);
x1com=(-b(u)+sqrt(b(u)^2-4*a*c(u)))/(2*a);
x2com=(-b(u)-sqrt(b(u)^2-4*a*c(u)))/(2*a);