Let's look at your data. You had a typo in the last element of mulasecc_result so I replaced the period with a comma.
num_injection = 15718;
SNR = [25, 30, 35, 40, 45, 50, 55, 60, 65, 70];
mulasecc_result = [3416, 7077, 10224, 12538,13969,14506,14687,14780,14841,14889];
plot(SNR, mulasecc_result)
Looking at this, it seems likely that following that curve from SNR = 25 to SNR = 0 will end up with an mulasecc_result value well below 0. Does that make sense for the process from which you obtained that data? Performing the extrapolation confirms that the value is quite negative.
SNR0 = interp1(SNR, mulasecc_result, 0, 'linear', 'extrap')
Remember what Mark Twain wrote in Life on the Mississippi, specifically chapter 17, about the potential dangers of extrapolation.
"In the space of one hundred and seventy-six years the Lower Mississippi has shortened itself two hundred and forty-two miles. That is an average of a trifle over one mile and a third per year. Therefore, any calm person, who is not blind or idiotic, can see that in the Old Oölitic Silurian Period, just a million years ago next November, the Lower Mississippi River was upwards of one million three hundred thousand miles long, and stuck out over the Gulf of Mexico like a fishing rod. And by the same token any person can see that seven hundred and forty-two years from now the Lower Mississippi will be only a mile and three quarters long, and Cairo and New Orleans will have joined their streets together, and be plodding comfortably along under a single mayor and a mutual board of aldermen. There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact."
