General improvements of the TimeVarying DCM planner

[GiulioRomualdi]

This PR introduces some general improvements for the TimeVarying DCM planner.

• 5da3568 convert the Casadi::MX element in Casadi::SX object. Thanks to this modification the desired DCM trajectory is computed faster.
  For instance, the test gives the following results:
  • Without the PR:

    ******************************************************************************
    This program contains Ipopt, a library for large-scale nonlinear optimization.
     Ipopt is released as open source code under the Eclipse Public License (EPL).
             For more information visit http://projects.coin-or.org/Ipopt
    ******************************************************************************
    
          solver  :   t_proc      (avg)   t_wall      (avg)    n_eval
           nlp_f  | 595.00us (  8.50us) 597.40us (  8.53us)        70
           nlp_g  |  56.22ms (803.11us)  22.99ms (328.42us)        70
        nlp_grad  |   1.91ms (  1.91ms) 727.76us (727.76us)         1
      nlp_grad_f  | 489.00us ( 19.56us) 493.73us ( 19.75us)        25
      nlp_hess_l  |  71.06ms (  3.38ms)  28.67ms (  1.37ms)        21
       nlp_jac_g  |  81.14ms (  3.01ms)  31.11ms (  1.15ms)        27
           total  | 501.12ms (501.12ms) 374.23ms (374.23ms)         1
    

  • With the PR:

    ******************************************************************************
    This program contains Ipopt, a library for large-scale nonlinear optimization.
     Ipopt is released as open source code under the Eclipse Public License (EPL).
             For more information visit http://projects.coin-or.org/Ipopt
    ******************************************************************************
    
          solver  :   t_proc      (avg)   t_wall      (avg)    n_eval
           nlp_f  | 815.00us ( 15.38us) 822.17us ( 15.51us)        53
           nlp_g  |   1.21ms ( 22.91us)   1.18ms ( 22.20us)        53
        nlp_grad  | 107.00us (107.00us) 106.85us (106.85us)         1
      nlp_grad_f  | 737.00us ( 32.04us) 738.33us ( 32.10us)        23
      nlp_hess_l  |   1.48ms ( 73.80us)   1.50ms ( 74.94us)        20
       nlp_jac_g  |   1.40ms ( 58.13us)   1.41ms ( 58.79us)        24
           total  | 276.92ms (276.92ms) 277.00ms (277.00ms)         1
    

• 393f668 introduces the possibility to switch the linear solver used by the IPOPT.
• f9a4cc3 improves the documentation

[GiulioRomualdi]

CI is failing on windows with this error that this not related with this PR

2020-10-03T02:13:45.5270628Z -- Acquiring MSYS2...
2020-10-03T02:13:45.5271845Z -- Downloading https://sourceforge.net/projects/msys2/files/Base/x86_64/msys2-base-x86_64-20190524.tar.xz/download...
2020-10-03T02:13:45.5273331Z -- Downloading http://repo.msys2.org/msys/x86_64/msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz...
2020-10-03T02:13:45.5275261Z -- Downloading http://repo.msys2.org/msys/x86_64/msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz... Failed. Status: 28;"Timeout was reached"
2020-10-03T02:13:45.5276616Z CMake Error at scripts/cmake/vcpkg_download_distfile.cmake:176 (message):
2020-10-03T02:13:45.5277185Z       
2020-10-03T02:13:45.5277545Z       Failed to download file.
2020-10-03T02:13:45.5278263Z       If you use a proxy, please set the HTTPS_PROXY and HTTP_PROXY environment
2020-10-03T02:13:45.5282223Z       variables to "***your-proxy-ip-address:port/".
2020-10-03T02:13:45.5283011Z       Otherwise, please submit an issue at https://github.com/Microsoft/vcpkg/issues
2020-10-03T02:13:45.5283441Z 
2020-10-03T02:13:45.5283740Z Call Stack (most recent call first):
2020-10-03T02:13:45.5284241Z   scripts/cmake/vcpkg_acquire_msys.cmake:86 (vcpkg_download_distfile)
2020-10-03T02:13:45.5284848Z   scripts/cmake/vcpkg_fixup_pkgconfig.cmake:281 (vcpkg_acquire_msys)
2020-10-03T02:13:45.5285431Z   ports/cppad/portfile.cmake:39 (vcpkg_fixup_pkgconfig)
2020-10-03T02:13:45.5285909Z   scripts/ports.cmake:79 (include)
2020-10-03T02:13:45.5286181Z 
2020-10-03T02:13:45.5286311Z 
2020-10-03T02:13:45.5286706Z Error: Building package cppad:x64-windows failed with: BUILD_FAILED
2020-10-03T02:13:45.5287284Z Please ensure you're using the latest portfiles with `.\vcpkg update`, then
2020-10-03T02:13:45.5287941Z submit an issue at https://github.com/Microsoft/vcpkg/issues including:
2020-10-03T02:13:45.5288478Z   Package: cppad:x64-windows
2020-10-03T02:13:45.5288819Z   Vcpkg version: 2020.06.15-nohash

Associated issue: microsoft/vcpkg#13286
cc @traversaro

[traversaro]

CI is failing on windows with this error that this not related with this PR

2020-10-03T02:13:45.5270628Z -- Acquiring MSYS2...
2020-10-03T02:13:45.5271845Z -- Downloading https://sourceforge.net/projects/msys2/files/Base/x86_64/msys2-base-x86_64-20190524.tar.xz/download...
2020-10-03T02:13:45.5273331Z -- Downloading http://repo.msys2.org/msys/x86_64/msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz...
2020-10-03T02:13:45.5275261Z -- Downloading http://repo.msys2.org/msys/x86_64/msys2-keyring-r21.b39fb11-1-any.pkg.tar.xz... Failed. Status: 28;"Timeout was reached"
2020-10-03T02:13:45.5276616Z CMake Error at scripts/cmake/vcpkg_download_distfile.cmake:176 (message):
2020-10-03T02:13:45.5277185Z       
2020-10-03T02:13:45.5277545Z       Failed to download file.
2020-10-03T02:13:45.5278263Z       If you use a proxy, please set the HTTPS_PROXY and HTTP_PROXY environment
2020-10-03T02:13:45.5282223Z       variables to "***your-proxy-ip-address:port/".
2020-10-03T02:13:45.5283011Z       Otherwise, please submit an issue at https://github.com/Microsoft/vcpkg/issues
2020-10-03T02:13:45.5283441Z 
2020-10-03T02:13:45.5283740Z Call Stack (most recent call first):
2020-10-03T02:13:45.5284241Z   scripts/cmake/vcpkg_acquire_msys.cmake:86 (vcpkg_download_distfile)
2020-10-03T02:13:45.5284848Z   scripts/cmake/vcpkg_fixup_pkgconfig.cmake:281 (vcpkg_acquire_msys)
2020-10-03T02:13:45.5285431Z   ports/cppad/portfile.cmake:39 (vcpkg_fixup_pkgconfig)
2020-10-03T02:13:45.5285909Z   scripts/ports.cmake:79 (include)
2020-10-03T02:13:45.5286181Z 
2020-10-03T02:13:45.5286311Z 
2020-10-03T02:13:45.5286706Z Error: Building package cppad:x64-windows failed with: BUILD_FAILED
2020-10-03T02:13:45.5287284Z Please ensure you're using the latest portfiles with `.\vcpkg update`, then
2020-10-03T02:13:45.5287941Z submit an issue at https://github.com/Microsoft/vcpkg/issues including:
2020-10-03T02:13:45.5288478Z   Package: cppad:x64-windows
2020-10-03T02:13:45.5288819Z   Vcpkg version: 2020.06.15-nohash

Associated issue: microsoft/vcpkg#13286
cc @traversaro

That error was fixed in microsoft/vcpkg#13889 . I am generating a new archive in https://github.com/robotology/robotology-superbuild-dependencies-vcpkg, but indeed there are regressions. For the time being I suggest to bump the vcpkg tag to 76a7e9248fb3c57350b559966dcaa2d52a5e4458 as done in robotology/robotology-vcpkg-ports#16 .

[GiulioRomualdi]

Thank you @traversaro. In e82a5e3 I bumped the vcpkg commit. Let's see if it solves the problem.

[GiulioRomualdi]

e82a5e3 fixes the problem. Merging