NumericalDiffEqs

From Sean_Carver
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Remember the equation for the cell with only leak channels.

 C \frac{dV}{dt} = I(t) - g_L(V - E_L)

Let's simplify: suppose there is no injected current and that the reversal potential for the leak channels is  E_L = 0 . Then our equation is

 \frac{dV}{dt} = - \frac{g_L}{C} V

Using different letters for the variables (because this is done in the software linked below):

 \frac{dy}{dt} = - k y

Here k is the rate constant, 1/k is the time constant, 1/k is  \frac{C}{g_L} = RC in the notation above. A leaky cell is what is called an RC circuit -- a resistor and capacitor together in a circuit. The time constant of an RC circuit is RC. The bigger k, the higher the rate of convergence, and the smaller the time constant 1/k. The time constant is the time it takes the solution to decay to 1/e of its value.

Solution of differential equations happens at discrete times:  y_k , separated by small time intervals dt.

The simplest way of solving this equation is with Euler's method:

 y_k = y_{k-1} + dt (k y_{k-1})

This is a special case of the general formula for Euler's method applied to the (vector) differential equation

 \frac{dy}{dt} = f(y)

 y_k = y_{k-1} + dt f(y_{k-1})

Click here for code for visualizing the numerical solution of differential equations.