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time shifting

Asked by ap singh on 20 Feb 2011

i want the program to advance or delay the signal... by taking input from user whether to advance or delay & by what number?.... please use switch statement?.... any signal like-ramp,step,exponential in it i am using subplot to plot the original signal & shifted version of the signal..

i have a program something like this--
*clear all
close all
clc
disp('given function is')
x=(-10:10);
for i=1:1:21
if(x(i)>0)
    y(i)=exp(x(i));
else
    y(i)=0;
end
end
subplot(1,2,1)
stem(x,y)
disp('enter whether to advance or delay')
s=input('1>advance\n 2>Delay')
n=input('enter the no of step by which signal is to be shifted')
switch(s)
case 1
    [
     for i=1+n:1:21+n
     if(x(i)>0)
     y(i)=1;
     else
     y(i)=0;
     end
    ]
case 2
    [
     for i=1-n:1:21-n
     if(x(i)>0)
     y(i)=1;
     else
     y(i)=0;
     end
    ]
subplot(1,2,2)
stem(x,y)

but when i run the program it gives error in the 'for' command in case 1.

3 Comments

Paulo Silva on 20 Feb 2011

What kind of signal and why use switch statement?
usually switch statements are for more complex problems.

Matt Tearle on 20 Feb 2011

Can you please explain in more detail what you're trying to do? Do you have a time base vector t and a signal y(t) and you want the user to input a dt... and then do... what with it exactly?

ap singh on 21 Feb 2011

i am begneer to matlab...
so Paulo Silva & Matt if you can help me in some more programs i will be very thankfull to u...

i need code to this programm
tell me the problem in the above program

thxs

ap singh

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5 Answers

Answer by Jan Simon on 21 Feb 2011
Accepted answer

Omit the square brackets around the case blocks and close the SWITCH and IF blocks with an END.

switch(s)
case 1
   for i=1+n:1:21+n
     if(x(i)>0)
       y(i)=1;
     else
       y(i)=0;
     end
   end
case 2
   for i=1-n:1:21-n
     if(x(i)>0)
       y(i)=1;
     else
       y(i)=0;
     end
   end
end

1 Comment

ap singh on 21 Feb 2011

will this program work??
is this right??...

Jan Simon
Answer by Walter Roberson on 21 Feb 2011

You cannot have an 'if' statement inside of [] . But you don't need to mark the beginning and end of the code for an individual case: all code is executed until the next 'case' or unmatched 'end'.

1 Comment

ap singh on 21 Feb 2011

ok but but my college sir told me that square [] are to be put so i put them.... now you hav told me to do it without brackets i will try it.. thnks

Walter Roberson
Answer by Matt Tearle on 21 Feb 2011

On top of the syntax issues Walter and Jan point out...

1. Why use switch? You could easily use a simple if/|else|. But why not just flip the sign of the offset. Something like n = sign(1.5-s)*n

2. You can make the unshifted signal in a couple of lines:

y = exp(x);
y(x<=0) = 0;

3. What you have in the switches will cause an error because it will try to reference x(22) (or higher), but x only has 21 elements. What are you trying to do here? I would have thought that what you want mathematically is y(x+dx). In which case you could repeat the above lines with a shifted x:

x2 = x + dx;
y = exp(x2);
y(x2<=0) = 0;

Also, what you have there sets y to just 0 or 1, rather than 0 or exp(x). Was that what you intended?

1 Comment

ap singh on 21 Feb 2011

yes sure i can..

but i am learning the use of the SWITCh statement...

Matt Tearle
Answer by ap singh on 21 Feb 2011

thanks to

Walter Roberson,Matt,Jan Simon,Paulo Silva for commenting & answering to my question!!!.....

meet u 2mmrw

0 Comments

ap singh
Answer by ap singh on 22 Feb 2011

as Jan Simon remove square brackets

i have written it like

clear all
close all
clc
disp('given function is')
x=(-10:10);
for i=1:1:21
if(x(i)>0)
    y(i)=exp(x(i));
else
    y(i)=0;
end
end
subplot(1,2,1)
stem(x,y)
disp('Enter whether to advance or delay')
s=input('1>advance\n 2>Delay=\n')
n=input('enter the no of step by which signal is to be shifted=')
switch(s)
case 1
     for i=1+n:1:21+n
if(x(i)>0)
    y(i)=exp(x(i));
else
    y(i+n)=0;
end
     end
case 2
     for i=1-n:1:21-n
if(x(i)>0)
    y(i)=exp(x(i));
else
    y(i-n)=0;
end
     end
end
subplot(1,2,2)
stem(x,y)

but still gives error as

" given function is Enter whether to advance or delay 1>advance 2>Delay= 1

s =

     1

enter the no of step by which signal is to be shifted=1

n =

     1

??? Attempted to access x(22); index out of bounds because numel(x)=21.

Error in ==> Untitled2 at 21 if(x(i)>0)"

please help...

1 Comment

Jan Simon on 22 Feb 2011

Do not access elements out of range:
for i=1+n:1:21+n
==>for i=1+n:min(21+n, length(x))
(a:1:b is the same as a:b)
and
for i=1-n:1:21-n
==>for i=1:21-n
You cannot access x(22) or x(0).

ap singh

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