Plot, if and elseif statement

Question

John 2011-4-6

Can some1 please help me with this.

Plot function f(x) over x=0:pi/10:2*pi

f(x)=sin(x) if (x<=pi)

f(x)=cos(x)+1 if (x>pi)

This is what I started so far and don't know what to do next.

x=0:pi/10:2*pi;

if x<=pi

xx=sin(x)

elseif x>pi

yy=cos(x)+1

end

Answer 1

Matt Fig 2011-4-6

IF statements do not pick out elements of an array as you are thinking they do. Use logical indexing.

x = 0:pi/10:2*pi;
y = zeros(size(x));
idx = x<=pi;
y(idx) = sin(x(idx));
y(~idx) = cos(x(~idx))+1; 
plot(x,y)

If you really want to use an IF statement, you will need to look element-by-element.

y = zeros(size(x));
for ii = 1:length(x)
   if x(ii)<=pi
     y(ii) = sin(x(ii));
   else
     % ...  fill it in.
   end
end

Matt Fig 2011-4-6

Should this be a FAQ? It seems like the

if x<3,...

construction for vectors is coming up all the time recently....