Calculate integral with an external formula
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I calculating an integral over a function that is defined in seperate m-file. My program looks like:
% main.m
mu_x=@(t) lx(t);
l_x = exp(-integral(@(t) mu_x(t),0,98));
% lx.m
function res=lx(x)
a=0.006782872;
b=5.44781E-08;
c=0.137849468;
if x>97
res = a+b*exp(c*97)+(x-97)*0.001;
else
res=a+b*exp(c*x);
end
I expect lx(x)=lx(98) => res=a+b*exp(c*97)+(x-97)*0.001; to be calculated but instead res=a+b*exp(c*x) is done. I want to keep this if-function in lx.m, is there anyway I can do this? Also, what is going wrong??
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Risposta accettata
David Goodmanson
il 11 Ott 2017
Modificato: David Goodmanson
il 11 Ott 2017
Hi Lenovo,
Your 'if' check is not working correctly, because the res function takes vector input for x. One way to do the task is to create an index that shows whether or not x > 97:
x = 0:.01:120;
plot(x,lx(x)) % demo
function res=lx(x)
a=0.006782872;
b=5.44781E-08;
c=0.137849468;
res = zeros(size(x));
ind = x>97;
res(ind) = a+b*exp(c*97)+(x(ind)-97)*0.001;
res(~ind) =a+b*exp(c*x(~ind));
end
3 Commenti
David Goodmanson
il 12 Ott 2017
I just plugged your expression
0.0067828+5.447812E-08*EXP(0.137849*97)+(98-97)*0.001
verbatim into Matlab, changed EXP to exp and got 0.0427, just like the demo plot in the posted answer gives and Excel gives. So I do not know where the .385 might be coming from.
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