question about the optimization result of rabbit example in FROST about frost-dev HOT 6 CLOSED

There could be a few cases this result happens:

1. your tau is not equals to 0 at the beginning of the domain;
2. you did not enforce the hybrid invariance constraints, i.e., y(0) = 0 and ydot(0) =0.

from frost-dev.

Ayonga, thanks so much for your reply! I thought for an orbit planning problem, every one will assume tau starts from 0. I also though if I do the hybrid trajectory optimization, the hybrid invariance constraint is the default setting.
So my next questions are:

1. how do I enforce tau starts from 0 and ends at 1
2. how to enforce the hybrid invariance constraints????
   I didn't see it in other examples. :(

from frost-dev.

I think the hybrid invariance constraint is enforced in
r_stance.UserNlpConstraint = str2func('right_stance_constraints');
r_impact.UserNlpConstraint = str2func('right_impact_constraints');
In the right_stance_constraints, the author have domain.VirtualConstraints.time.imposeNLPConstraint(nlp, [bounds.time.kp, bounds.time.kd], [1,1], load_path); . but the results is still not correct.
I think it can be the tau is not start from 0, how do I check the range of the tau in the optimization result? Have no clue :(

from frost-dev.

@ayonga
I have just tried the default version for rabbit optimization. I did not modified anything. The phase variable is time based.
In the results, params{1,1}.ptime=[0.4956,0]., and the tspan is from 0 to 0.4956. Based on the definition of tau=(t-p(2))/(p(1)-p(2)), it should start from 0 to 1;
Then based on what you said, the problem should be the enforcement of hybrid invariance constraints, but in the code right_stance_constraints.m, it does set the constraint. Then everything thing should be good. However, the result still doesn't make sense.
The first column of x is
-0.1678 0.7400 0.1690 2.4270 0.6454 2.9454 0.5880
the coefficients of Bezier curve are :
2.4271 0.6455 2.9453 0.5880 2.5426 0.5941
2.9781 0.7263 2.6988 0.4451 2.8123 1.0771
2.7080 0.5621 2.5740 1.1960 2.8510 0.4166
2.3711 1.0778 2.9458 0.5877 2.4274 0.6458.
As you can see, the first coefficient of first Bezier curve is really close to x(4), whick make sense, however, the rest looks bad to me. Is there any bug on that existing rabbit example? I really can not figure it out myself.
Thanks you!

from frost-dev.

You did not correctly reformat the Bezier coefficient, you should use reshape(params{1}.atime,4,6), which will give you
2.4269 2.5425 2.6987 2.7077 2.8508 2.9457
0.6454 0.5941 0.4452 0.5623 0.4165 0.5875
2.9453 2.9781 2.8124 2.5739 2.3709 2.4272
0.5879 0.7262 1.0771 1.1959 1.0778 0.6458
where the first column of x would be:
-0.1678
0.7400
0.1692
2.4269
0.6454
2.9453
0.5879
.

from frost-dev.

Thank you so much! That is simply awesome! I think we can close this case for now.. Orz

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