# multiplication of functions integration problem

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fima v on 7 May 2020
Edited: fima v on 11 May 2020
Hello,i have two functions "fun" and "coef_fun"
"coef_fun" was created with interpolation of the attached CSV and it looks like in the photo bellow.
I have integrated fun over some interval ,and i got some numeric result.
When i tried to integrate the multiplication of fun and coeff_fun (in order to see the reduction the the numeric result)
It gives me an error "Undefined operator '*' for input arguments of type 'function_handle'"
i have attached my code.
Where did i go wrong in integrating multiplication of functions?
Thanks.
%Default Dataset_new file
x = data(:,1);
y = data(:,2);
%plot(x,y);
data_x1=x*0.000001; %transform to micron
[data_k, index] = unique(data_x1);

ChrizzzlP on 7 May 2020
mult_fun needs to be defined as a function too. simple example below:
fun = @(x)x+3;
coef_fun = @(x) 5*x+9;
multiplication_func = @(x) fun(x)*coef_fun(x);
multiplication_func(2)

Steven Lord on 7 May 2020
You can't multiply function handles.
multiplication_formula = @(lambda) fun*coef_fun;
You can multiply the values you receive when you evaluate function handles.
multiplication_formula = @(lambda) fun(lambda).*coef_fun(lambda);
I switch to using element-wise multiplication (the .* operator) instead of the matrix multiplication operator (the * operator) because I see you're passing this function handle multiplication_formula into integral. Generally you want to use the element-wise operators in functions you're going to pass into integral, ode45, and similar functions.
fima v on 7 May 2020
Hello Steven when i did the "fun" ONLY integration,fun_integral results in 43
But when i integrate the element wise multiplication you suggested( which is adding a filter and it should reduce the integral result)instead i get NAN in the mult_integral.
it said "Warning: Infinite or Not-a-Number value encountered"
Why my integral exploded?
What could be done?
Thanks
x = data(:,1);
y = data(:,2);
%plot(x,y);
data_x1=x*0.000001; %transform to micron
[data_k, index] = unique(data_x1);
fima v on 7 May 2020
Hello I was able to integrate the Purple plot over the range and it gave me 43
Why when i integrate the smaller green plot My integral explodes?
Thanks.