while loop: how to define a function when using equation with several variables?

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Sandie Nhatien Vu
评论： Sandie Nhatien Vu 2016-8-6
So. I have this function as the bacteria growth:
n (t+1) = n(t) * (1 + (alpha*(1-(n(t)/K))))
The template for the function should look like this:
function tN = bacteriaGrowth(n0, alpha, K, N)
where n0 = initial number of bacteria (scalar)
alpha = growth rate (scalar)
K = capacity (scalar)
N = final population size (scalar, no < N < K)
tN = Time t at which population size exceeds N (scalar)
So I want to write a function that simulates the bacteria growth hour by hour and stops when the number of bacteria exceeds some fixed number, N. It must return the time t at which the population first exceeds N.
Ex: function tN = bacteriaGrowth(100, 0.4, 1000, 500) will give the output: 7
because: n0 = 100, n1 = 136, n2 = 183, n3 = 242.8, n4 = 316.3, n5 = 402.9, n6 = 499.1, n7 = 599.1, n8 = 695.2
I came up with this code, but it seems to require some (or many) adjustments.
function tN = bacteriaGrowth(n, alpha, K,N)
n = 0;
tN = 0;
tN_after = 0;
while n < N < K
tN = n(t) * (1 + (alpha*(1-(n(t)/K))))
n = n + 1;
tN_after = tN;
fprintf('%.4f\n', tN_after)
end

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采纳的回答

Walter Roberson
Walter Roberson 2016-8-6
You are not changing t in your loop, so you would not be able to output the time.
while n < N < K
is the same as
while ((n < N) < K)
the first expression n < N will return either false, 0, or true, 1, so you would be checking either 0 < K or 1 < K . It is unlikely that is what you mean.
Your equation models an exponential growth. Exponential growth requires that there be something to start with, but you are initializing your population size to 0, and exponential growth from 0 is always going to remain 0.
What is the point of having parameters to a function, such as n, if you are going to overwrite them in the function without paying attention to them?

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