Why my normpdf in not working??

Hey, why my normpdf func gives just 0 values?

tempg is 15x1 double :

509.068900000000

516.481400000000

521.696500000000

524.645900000000

524.815600000000

526.077300000000

529.092400000000

532.904900000000

534.609900000000

535.836600000000

555.625600000000

562.575200000000

564.946200000000

570.851500000000

587.199300000000

templm is 15x1 double :

472.553000000000

474.792900000000

477.094100000000

479.618700000000

482.186900000000

496.408900000000

497.575800000000

498.234600000000

498.238900000000

499.949700000000

505.844600000000

508.283500000000

509.053700000000

518.186900000000

519.404700000000

devgd = std(tempgd);
devlm = std(templm);


ygd = normpdf(tempgd)
ylm = normpdf(templm)

subplot(2,1,1)
plot(tempgd,ygd)
%axis([420 620 0 0.02])



subplot(2,1,2)
plot(templm,ylm)
%axis([420 620 0 0.012])

Answer 1

[Steven Lord]

Let's evaluate the PDF using the formula in the documentation for normpdf at that large x value. I'll choose the smallest value in your two vectors.

x = sym(472.553);
sigma = 1;
mu = 0;
f = (1/(sigma*sqrt(2*pi)))*exp(-(x-mu)^2/(2*sigma^2))

f = 

How small is that?

vpa(f)

ans = 

1.7610343601779488103423727433985e-48491

Yeah, that definitely underflows in double precision.

If you specified the mean (I'm going to estimate it as roughly 495) then the value of the PDF will be quite a bit larger.

sigma = 495;
vf = vpa((1/(sigma*sqrt(2*pi)))*exp(-(x-mu)^2/(2*sigma^2)))

vf = 

0.00051098157878291063575577801991873

[Maciej Dawczak]

So what to do to get normal distribution of that data?