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# Trapezoidal method

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## Trapezoidal method

(OP)
Hello,
I am working on a program to find the value of the current in a coil. This value satisfies the following equation:
y'=sin(2t)-[(ey-1)/(ey+1)]

which is of the form y'=f(t,y)

I know that in order to solve this I need to use the trapezoidal method to solve a differential equation, the formula is:
yn+1=yn+.5*h(f(tn,yn)+f(tn+1,yn+1) where h=tn+1-tn

I have found examples of the standard trapezoidal method but I do not think they will help because of the difference in the formulas. Can anybody give me some guidance here?

### RE: Trapezoidal method

Do you need guidance in the math or the programming?

### RE: Trapezoidal method

the programming, I know how the math behaves but I am unfamiliar as far as how to write this in C++ code.

### RE: Trapezoidal method

I am totally ignorant as to what is required. Do you need a load of y values given a set of t values or the y and t value when they satisfy some condition like y' is zero. I also don't really know how you would solve something like

yn+1=yn+.5*h(f(tn,yn)+f(tn+1,yn+1)

because yn+1 appears on both sides. Assuming h is really small, why not use the Euler form of

y(n+1) = yn + h * f(tn, yn)

In that case, the same question arises: do you want all the values given a starting t0 and y0 up to a particular value of tn or do you just want it satisfying some criteria.

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