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How does the following two codes differ? both are working, but they are yielding different answers

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Hello,
Could you explain for me why I'm not getting the same answer from the following two codes??
function whatswrong(x)
x1= linspace(0,x);
n=length(x1);
uy = -5/6.*(sing2(x1,0,4)-sing2(x1,5,4))...
+ 15/6.*sing2(x1,8,3) + 75*sing2(x1,7,2)...
+ 57/6.*x1^3 - 238.25.*x1;
plot(x1,uy,'--')
xlabel('x1')
ylabel('uy'),
title('displacement versus distance')
function check = sing2(x1,a,n)
if x1 > a
check = (x1 - a).^n;
else
check=0;
end
------------------------------------------------------------------------------------------------------
function beam2(x)
x1= linspace(0,x);
n=length(x1);
for i=1:n
uy(i) = -5/6.*(sing(x1(i),0,4)-sing(x1(i),5,4));
uy(i) = uy(i) + 15/6.*sing(x1(i),8,3) + 75*sing(x1(i),7,2);
uy(i) = uy(i) + 57/6.*x1(i)^3 - 238.25.*x1(i);
end
plot(x1,uy)
function check = sing(x1,a,n)
if x1 > a
check = (x1 - a).^n;
else
check=0;
end
many many thanks,

Risposta accettata

Roger Stafford
Roger Stafford il 15 Mar 2015
In the functions 'sing' and 'sing2' you have "if x1 > a". If x1 is a many-element vector, this only comes true what all elements are greater than a. Since you are presenting 'sing' with a scalar x1 one at a time and 'sing2' with a vector, you will get different results from them. You need to rewrite 'sing2' if you want the vectorized 'whatswrong' to work properly.
Also in 'whatswrong' you have written x1^3 where x1 is a vector and that should give you an error message, not a result. I assume you didn't actually run it that way if you got a result.
  3 Commenti
Roger Stafford
Roger Stafford il 15 Mar 2015
It can be written in vectorized form as:
function check = sing2(x1,a,n)
check = (x1>a).*(x1-a).^n;
end
If you prefer a for-loop, it could be:
function check = sing2(x1,a,n)
check = zeros(size(x1));
for k = 1:length(x1);
if x1(k) > a
check(k) = (x1(k)-a)^n;
end
end
end
Note that in this second method the condition after the 'if' gets applied one at a time and therefore gives you the same result as obtained with your use of 'sing'.

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