Array indices must be positive integers or logical values.

I tried to declare an if so that it would calculate a sign change in a vector and show the results but I get this error. If someone helps me I would be grateful

this is my code, variables min and max are introduced by user, i suposed is an error in the declaration of array but i don't know how fix it

tam=(min*-1)+xmax+1;
xi=(tam);
fxi=(tam);

for i=min:1:xmax
xi=min;

fev=inline(fx,'x');
fxi=fev(xi);

format long
r=sprintf('f( %d ) = %d', xi, fxi);
disp (r);

min=min+1;   
end

disp(tam)

x1=0;
x2=0;
y1=0;
y2=0;

n=0;
for i=n:1:tam-1
   
   if  xi(n)*xi(n+1)<0
      pos=i;
      pos2=i+1;
      y1=xi(pos);
      y2=xi(pos2);
      x1=fxi(pos);
      x2=fxi(pos2);
      
      disp(pos+1);
      disp(pos2+1);
      
      disp(x1);
      disp(x2);
   end    
end    

Answer 1

[James Tursa]

n = 0 and then you use it as an index:

n=0;
for i=n:1:tam-1
   if  xi(n)*xi(n+1)<0

You can't have a 0 index.

Also, min is the name of a MATLAB function ... it would be best if you picked a different name for your variable, such as xmin.

[Julio Soto]

yeah, i tried but i get the same error (

Array indices must be positive integers or logical values.

Error in title (line 53)

if (xi(n))*(xi(n+1))<=0 )

i'm principiant and i'm learning alone

I ask me if exist an easy form to do operations with the value into an especific position of vector. I try to convert code of java to an matlab script, this is the part that i try to implement

rfx is an array his lenght is declareted for a sum of two values writen by the user

for (int it=0; it<rr-1;it++){

if( rfx [ it ]*rfx [ it+1 ]<=0){

int pos=it;

int pos2=it+1;

y1=rfx[pos];

y2=rfx[pos2];

xx1=rfxi[pos];

xx2=rfxi[pos2];

System.out.println("Solucion");

System.out.println(pos+1);

System.out.println(pos2+1);

[James Tursa]

java is 0-based indexing but MATLAB is 1-based indexing. You will need to add 1 to all of your indexing in your MATLAB code.

Answer 2

[Image Analyst]

Finally. I was wondering when this question would come in today. So here is the link to this very faqqy of faqs:

https://matlab.fandom.com/wiki/FAQ#.22Subscript_indices_must_either_be_real_positive_integers_or_logicals..22

Also wondering if you tried n = 1 or got rid of it entirely

for k = 1 : length(xi) - 1   
   if  xi(k)*xi(k+1) < 0
      pos = k;
      pos2 = k + 1;      

Of course it could be even better.