if statements inside a function file and the function called by a for loop

hi every body im new in matlab and i have this script

clear all
format long 
k=100; 
dx=1; 
x=zeros(k,1);
y=zeros(k,1);

x(1)=1; 
for n=2:k;  
  x(n)=x(n-1)+dx; 
  [ y ] = test( x );
end 
tb=[x(1:k) y(1:k)]

and this function file

function [ y ] = test( x )
if x<25
  y=x*2;
elseif x>25
  y=x*10; 
else 
  y=x*1000;
end

when i run it just the

else 
  y=x*1000;
end

part is evaluated, and i want all the x(n) be evaluated in the correct if.

what im doing wrong?

[Walter Roberson]

Why does your program start with "clear all" ??

Answer 1

[Walter Roberson]

http://www.mathworks.com/help/matlab/ref/if.html

An evaluated expression is true when the result is nonempty and contains all nonzero elements (logical or real numeric). Otherwise, the expression is false.

What are you testing? x<25.

How big is x?

Does x<25 result in all non-zero elements?

Answer 2

[Roger Stafford]

When you write "y=test(x)" rather than "y=test(x(n))" or "y=test(x(n+!))", you are passing 'test' an x vector with 100 elements in it and the resulting y will also have 100 elements. At the 'if' and 'elseif' points in 'test' each would always require that the given condition hold for all hundred cases of x and that is never true. Hence only the 'else' part is ever executed. Look up the documentation on 'if' and 'elseif'.

[MEXICO]

ok, im trying to understand (sorry, its cuz my english :S), you are saying that in each if else and else if point the vector x that is 100 is evaluated, so the last statement "else" that is bigger than 25 is always evaluated because x is equal to 100?. so, i have to write "y=test(x(n)) instead of y=test(x). and in the function file i have to use x(n) too?

thanks for the help and your time =)

[Walter Roberson]

Yes, x(n). And assign the result to y(n)

Answer 3

[MEXICO]

thanks for the answers, this is just a test of a complex function , but my problem is in the if statements. x is a vector 1:k (k=100) with initial condition x(1)=1, and the function test is composed by a 3 equation where the x's lower than 25 are evaluated in the first if, bigger than 25 in the second and else's in the thirth, the results of the iterations at each case (if's) are listed in tb=[x(1:k) y(1:k)]. but when i run it, just the last else are where the x's are evaluated. so, what i want is n numbers of values of x's be evaluated in the function test where exist 3 equatios for 3 diferent cases of magnitude of x's. =)

[Walter Roberson]

Please look in the MATLAB documentation for information about logical indexing.