Anatoly - 2 months ago 23

C Question

I'm in process of writing program for equation simplifications. In this program in want to use binomial and trinomial theorems.

With binomial expansion:

*(x+y)^r*

*Sum(k -> r) x^[r-k] y^[k]*,

where k is 0 and r is degree of binomial.

I can do it like this:

`for (k=0; k<=r; k++) {`

x_degree=r-k;

y_degree=k;

}

Otherwise, if i want to implement trinomial theoreme i should satisfy constraints of form:

where n is degree of trinomial and i+j+k=n.

I think about it for a while, but i can't figure out something better than loop through all possible combinations, as follows:

`for (int i=0; i<=n; i++)`

for (int j=0; j<=n; j++)

for (int k=0; k<=n; k++) {

if((i+j+k)==n) {

find_coefficient(i,j,k);

set_degree_values(i,j,k);

proceed();

}

}

So my questions is:

Thank you.

Answer

Taking the fourth degree as an example, the powers of the three variables can be listed as

```
004, 013, 022, 031, 040,
103, 112, 121, 130,
202, 211, 220,
301, 310,
400
```

The logics is to decrement the rightmost digit and increment the one to its left. When the latter reaches `r`

, you increment the one to its left and reset the right digits (that's a modified carry operation).

This scheme can be implemented by means of `n`

counters and generalizes to the multinomial theorem. I wouldn't be surprised that the coefficients can be computed incrementally as well. (Actually, the counters will simulate nested loops.)

Source (Stackoverflow)

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