Printing matrices in casadi

[yugiero]

Hi!

I was wondering why it is not possible to print vectors/matrices when working with a casadi model using .to_array(). Is there another option to do that?
A minimal example:

import numpy as np
import biorbd
import biorbd_casadi as casadi

model = biorbd.Model("pendulum.bioMod")
q = np.array([[1,2,3,4],[1.1,2.1,3.1,4.1],[1.2,2.2,3.2,4.2]])
com = model.CoM(q[0]).to_array()
print(com)

model = casadi.Model("pendulum.bioMod")
q = np.array([[1,2,3,4],[1.1,2.1,3.1,4.1],[1.2,2.2,3.2,4.2]])
com = model.CoM(q[0]).to_array()
print(com)

[pariterre]

Hi there!
Casadi does not actually carry actual data, but graph of the code that can generate the results of a computation. Therefore, it is sort of meaningless to get the array, as MX are graphs. Henceforth, there is no such thing as to_array(), but you can get the graph using to_mx().

That said, you can evaluate the graph. You must, however, first convert the graph (the MX) to a casadi.Function and then you can call that very function to evaluate the graph. I made an easy interface to convert to casadi.Function in Python. It would look something like:

import biorbd_casadi as casadi
from casadi import MX
import numpy as np

# Get a model
model = biorbd.Model("pendulum.bioMod")

# Create a symbolic variable of dimension (nq x 1) that will be used to create the graph
q_symbolic = MX.sym("q", model.nbQ(), 1) 

# Create the casadi function
com_func = biorbd.to_casadi_func('com', model.CoM, q_symbolic)  # Alternatively you can create yourself the function using casadi.Function

# Evaluate the graph with actual data
q = np.random.rand(model.nbQ())  # This can also be casadi.DM
com = com_func(q)  # This a DM, but can be converted to array using "com = np.array(com)"
print(com)

Hope this helps!

[yugiero]

Interesting, thanks a lot!