residual function

[cmichelenstrofer]

The hydrodynamic bodies's residual constraint is built in the core solver. One can recreate it with the post-processed time-series, but it might be useful to just supply a function that does this calculation. The main residual (and any other equality constraint) could also be printed during the optimization output.

[ryancoe]

@cmichelenstrofer - I'm a bit confused by your comment above. The scaled residual function is indeed created in wot.solve,

WecOptTool/wecopttool/core.py

Lines 766 to 770 in 6c9b852

	# system dynamics through equality constraint, ma - Σf = 0
	def scaled_resid_fun(x):
	x_s = x/scale
	x_wec, x_opt = self.decompose_state(x_s)
	return self._resid_fun(x_wec, x_opt, waves)

but there is a hidden function for the residual equation that a user can call

WecOptTool/wecopttool/core.py

Lines 604 to 612 in 6c9b852

	def _resid_fun(self, x_wec, x_opt, waves):
	if not self.inertia_in_forces:
	ri = self.inertia(self, x_wec, x_opt, waves)
	else:
	ri = np.zeros([self.ncomponents, self.ndof])
	# forces, -Σf
	for f in self.forces.values():
	ri = ri - f(self, x_wec, x_opt, waves)
	return self.dofmat_to_vec(ri)

[cmichelenstrofer]

@ryancoe yes, you are right! I suggest we make it a regular function (not a hidden one). And check that we can use it (e.g. as callback) to print out the value during the solve. This is something @gbacelli has asked for a few times. Should give us insight into the convergence of the optimization.

[cmichelenstrofer]

• changed the residual function to be non-hidden.
• fixed a bug with callback (state x was not being scaled)

To print all the residuals (each DOF at each time step) you can do something like this:

def callback(wec, x_wec, x_opt, waves):
    wot._log.info(f"dynamic equation residual: {wec.residual(x_wec, x_opt, waves)}")
    return 

or to just check if it is satisfied:

def callback(wec, x_wec, x_opt, waves):
    wot._log.info(f"dynamic equation residual: {np.allclose(wec.residual(x_wec, x_opt, waves), 0)}")
    return 

The callback is called after each iteration. I tried it with Tutorial 1 and the condition is satisfied after the first iteration (never prints false).

Similarly the callback could include user defined constraints functions.