Question

Error using ==> mpower . Matrix must be square.

Asked by: YANKAUSKAS

Why do we need the period before the ^ operator but not in other? IF the function is x^2- x*sin(x), do we need the period before the * in x*sin(x);

I'm in need of the answer, asap!
 Thank you very much!

f=inline('x.^2-4*sin(x)');
df=inline('2*x-4*cos(x)');
esp=input('esp =');
x=0.5:0.01:3.5;y=f(x);
plot(x,y); hold on;
x=[];y=[];
x=[x 3]; y=[y f(x(1))];
i=2;
while abs(x(i)-x(i-1))>2*esp
    i=i+1;
    x=[x x(i-1)-f(x(i-1))/df(x(i-1))];
    y=[y f(x(i))];
    plot(x(i),y(i),'rp')
    fprintf('\n\t%f\t%f',x(i),f(x(i)));
end
plot(x(end),f(x(end)),'*'); hold off;

                                  
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Asked On
2008-07-11 at 11:29:28ID23558168
Tags

MATLAB

,

2008RB

Topic

MatLab Programming Language

Participating Experts
1
Points
500
Comments
3

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Answers

 

by: YANKAUSKASPosted on 2008-07-11 at 11:38:10ID: 21984849

Why in this code below, we don't have to use the period before ^?

f=inline('x^2-3*x+2'); fdh=inline('2*x-3'); 
x(1)=start; y(1)=f(start) ; ydh(1)=fdh(start); 
x(2)=x(1)-y(1)/ydh(1); 
done=0; i =1; 
while ~done  
    x(i+1)=x(i)-f(x(i))/fdh(x(i)); 
    y(i+1)=f(x(i)); 
    if abs(x(i+1)-x(i))<tol , done=1; 
    end 
    i=i+1; 
end 
root =x(i); 

                                              
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by: LukeyJayPosted on 2008-07-13 at 13:44:47ID: 21994132

When 'x' is a vector or a matrix, just writing something like

x^2

makes matlab think you want to square a matrix, which is only possible with square matrices.  If you have a row vector, then you have a 1 x N matrix, so unless N = 1, you don't have a square matrix, and you get an error.  If you merely want to square each entry in x, then you use the " .^ " operator to indicate point-by-point operations (such as division, multiplication, or raising to a power).  Whether you need the "dot" before the symbol (/ * or ^) depends on what you're doing.  From the looks of it to me, you need the dot if you have a row vector that you only want to use to simulate continuous time.

Luke

20120131-EE-VQP-002

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