Logarithmic plot of function using pchip

Hello,

I got a problem with plotting a graph from distinct pairs of values.

My Code:

dil2f = [1 50 100 200 500 1000 2000 4000];
dil2an = [70.24 31.21 19.88 11.56 5.11 2.65 1.35 0.68];


xi = 0:.1:4000;
hold on;

Z1 = pchip(dil2f, dil2an, xi);

plot(xi, Z1);

xlabel("n [connections/day]");
ylabel("t_{lt} [years]");

set(gca, 'XScale', 'log')
set(gca, 'YScale', 'log')

xlim([1 4000])
grid on
grid minor

xticks([1 10 100 1000 4000])
xticklabels({'10^0', '10^1','10^2','10^3','4*10^3'})

which gives me this result:

As you can see the curve is not really smooth and seems to "wobble".

Am i using the wrong method for interpolation? Or do i miss something because of the logarithmic scale?

I am gladful for some help!!

Thanks in advance!

Answer 1

[Jonas]

try interpolation in logarithmic space:

Z1 = 10.^(interp1(dil2f, log10(dil2an), xi,'pchip'));

or

Z1 = 10.^(pchip(dil2f, log10(dil2an), xi));

it looks already better than in your figure, you can try different methods in the interp1 function