Houdini - A solver is a reduce function

A solver is essentially a reduce function. It’s passed, as its first argument, the result of the previous loop’s evaluation.

A reduce function in Javascript:

const array1 = [1, 2, 3, 4];
function reducer(accumulator, currentValue) { return accumulator + currentValue } ;

result = array1.reduce(reducer) //=> 10

Inside a solver:

As an example, we create a network with a single attribute @num = 0 and pass it into the solver.

Inside the solver network, all we do is add +1 to the @num attribute and return it:

The Wrangle has the code:

@num = @num + 1; // Or simply "@num += 1"

So, on each frame, the solver is passed the result of the previous frame, adds 1 to it and returns it to the next iteration.

And we end up with this:

Note

The “activated” node inside a solver network is the “return value” of the function. Activating the Prev_Frame node means the function always evaluates to the very first initial argument that was passed into it – in this case, @num == 0 always.