Linking acados with external libs

byfra · February 13, 2020, 10:09pm

Hi,
I’m trying to move my OC problems from Casadi/Ipopt to Acados.
So far, so good !
But I stumbled upon the following issue :
my ode function is given by an external .so lib which I load thanks to :
f_ext = casadi.external("my_ext_func", "my_ext_func.so", {"enable_fd"=True})
f_expl = f_est(x,u)
model.f_expl_expr = f_expl
When compiling, I get the following error :
OSError: c_generated_code/libacados_ocp_solver_eocar_ode.so: undefined symbol: my_ext_func
Which I understand, but since the makefile is automatically generated, how should I specify Acados to link with external libs, if this is possible ?!
Thank you,
Fb

FreyJo · February 14, 2020, 10:05am

Hi,
I have to admit, that I never linked additional external libraries for the model functions and there is no workflow for this in the template yet.
But, I think I can point out how it should work.

To be clear, you only have to link this external function my_ext_func.so to the shared library containing your ocp solver libacados_ocp_solver_eocar_ode.so, not the acados shared library.

The Makefile is generated from this template:

github.com

acados/acados/blob/master/interfaces/acados_template/acados_template/c_templates_tera/Makefile.in

#
# Copyright 2019 Gianluca Frison, Dimitris Kouzoupis, Robin Verschueren,
# Andrea Zanelli, Niels van Duijkeren, Jonathan Frey, Tommaso Sartor,
# Branimir Novoselnik, Rien Quirynen, Rezart Qelibari, Dang Doan,
# Jonas Koenemann, Yutao Chen, Tobias Schöls, Jonas Schlagenhauf, Moritz Diehl
#
# This file is part of acados.
#
# The 2-Clause BSD License
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
# 1. Redistributions of source code must retain the above copyright notice,
# this list of conditions and the following disclaimer.
#
# 2. Redistributions in binary form must reproduce the above copyright notice,
# this list of conditions and the following disclaimer in the documentation
# and/or other materials provided with the distribution.
#

This file has been truncated. show original

I think you just have to modify this command by adding the linker flag to your external function.

github.com

acados/acados/blob/acc48e0708d18af2cf4401519a736b361d8ba0b8/interfaces/acados_template/acados_template/c_templates_tera/Makefile.in#L200


CASADI_COST_R_SOURCE=
CASADI_COST_R_E_SOURCE=
{% if cost_type == "NONLINEAR_LS" %}
CASADI_COST_R_SOURCE+= {{ model.name }}_r_cost.c 
{% endif %}
{% if cost_type_e == "NONLINEAR_LS" %}
CASADI_COST_R_E_SOURCE+= {{ model.name }}_r_e_cost.c 
{% endif %}


casadi_fun:
	( cd {{ model.name }}_model; gcc $(ACADOS_FLAGS) -c  $(CASADI_MODEL_SOURCE))
	{% if constr_type == "BGP"  and dims_nphi > 0 %}
	( cd {{ model.name }}_constraints; gcc $(ACADOS_FLAGS) -c  $(CASADI_CON_PHI_SOURCE))
	# ( cd {{ model.name }}_constraints; gcc $(ACADOS_FLAGS) -c  $(CASADI_CON_R_SOURCE))
	{%- endif %}
	{% if constr_type_e == "BGP"  and dims_nphi_e > 0 %}
	( cd {{ model.name }}_constraints; gcc $(ACADOS_FLAGS) -c  $(CASADI_CON_PHI_E_SOURCE))
	# ( cd {{ model.name }}_constraints; gcc $(ACADOS_FLAGS) -c  $(CASADI_CON_R_E_SOURCE))
	{%- endif %}
	{% if constr_type == "BGH" and dims_nh > 0 %}
	( cd {{ model.name }}_constraints; gcc $(ACADOS_FLAGS) -c  $(CASADI_CON_H_SOURCE))

You could add something like:

	{%- if not model_external_shared_lib == "" %}
	-I {{ model_external_shared_lib }}
	{% endif %}

You could first try to edit the rendered Makefile by adding such a line.
If it works, it would be great if you make a pull request with that.
Note, you always have to reinstall the Python interface if you change the templates or the Python code.

Let me know if this somehow works for you.

Best,
Jonathan

FreyJo · February 15, 2020, 12:13pm

Hey @byfra,

I realized it might be a bit much to ask you to make these changes, so I just did it myself.
Could you try to check out this version and let me know if that works for you?

Best,
Jonathan

byfra · February 15, 2020, 1:12pm

Hi FreyJo !

I actually did the mods yesterday and it works just fine. I can push them on my fork and request a pull so you can inspect it or I can test your version. Let me know what you prefer.

François

FreyJo · February 15, 2020, 3:46pm

Hi François,

awesome!
For me both options work.
Just either comment on my PR or do another one with your change and I will review it.

Best,
Jonathan

byfra · February 15, 2020, 4:14pm

I’ll let you review mine
Thanks !

FreyJo · February 25, 2020, 12:43pm

Merged, thanks for collaborating