Call specific expression index from a function carrying multiple expression

I had defined a function

function y=func (x)
 y=[x;x.^2];

Now I have to integrate each expression i.e. x and x^2 for different limits. Eg. quad('x',1,5) and quad('x^2',5,9)..How can we do this using the function as defined earlier?

Answer 1

[Walter Roberson]

Break it up in to two different integrations with different functions and add the two results together.

You can use helper functions such as

row1 = @(x) x(1,:);
row2 = @(x) x(2,:);
quad(@(x) row1(f(x)), 1, 5) + quad(@(x) row2(f(x)), 5, 9)

[Piyush Pallav]

Is there any way to get around from defining row1, row2? As the function 'func' is user defined and so it may contain any number of expressions. I wanted a vectorised rows

[Walter Roberson]

row_n = @(x,n) x(n,:);
quad(@(x) row_n(f(x),1), 1, 5) + quad(@(x) row_n(f(x),2), 5, 9);

Or perhaps you would prefer

partsbounds = [1 5 9 10 15];  %break-points
fun_select = [1 2 2 1];       %which subresult for each range

total_integral = 0;
for K = 1 : length(fun_select)
  total_integral = total_integral + quad(@(x) run_n(f(x), fun_select(K)), partsbounds(K), partsbounds(K+1));
end

... and I suspect that I've just done someone's homework assignment :(

[Piyush Pallav]

Haha..Thank you..I hope next time I will ask the question after the homework assignment is over ;)