homebrewでOctave(version 4.2.1)をインストールした時に、tf2pzが使えない問題の解消

Octave-Forgeのパッケージのsignal, controlが入っていないことが原因。しかし、
```
octave:1> pkg install -forge signal control
```
を実行すると以下のエラーが出る。

```terminal
octave:1> pkg install -forge signal control
In file included from __control_helper_functions__.cc:7:
./lti_input_idx.cc:65:48: warning: 'nelem' is deprecated [-Wdeprecated-declarations]
    octave_idx_type len = args(0).cell_value().nelem();
                                               ^
/usr/local/Cellar/octave/4.2.1_6/include/octave-4.2.1/octave/Array.h:360:19: note: 'nelem' has
      been explicitly marked deprecated here
  octave_idx_type nelem (void) const { return numel (); }
                  ^
1 warning generated.
clang: warning: argument unused during compilation: '-pthread' [-Wunused-command-line-argument]
In file included from __control_slicot_functions__.cc:24:
./sl_tg04bx.cc:79:33: warning: 'length' is deprecated [-Wdeprecated-declarations]
        octave_idx_type ip = pr.length ();  // ip: number of finite poles
                                ^
/usr/local/Cellar/octave/4.2.1_6/include/octave-4.2.1/octave/Array.h:354:19: note: 'length' has
      been explicitly marked deprecated here
  octave_idx_type length (void) const { return numel (); }
                  ^
In file included from __control_slicot_functions__.cc:24:
./sl_tg04bx.cc:80:33: warning: 'length' is deprecated [-Wdeprecated-declarations]
        octave_idx_type iz = zr.length ();  // iz: number of zeros
                                ^
/usr/local/Cellar/octave/4.2.1_6/include/octave-4.2.1/octave/Array.h:354:19: note: 'length' has
      been explicitly marked deprecated here
  octave_idx_type length (void) const { return numel (); }
                  ^
In file included from __control_slicot_functions__.cc:42:
./sl_ident.cc:184:40: warning: 'nelem' is deprecated [-Wdeprecated-declarations]
        octave_idx_type n_exp = y_cell.nelem ();            // number of experiments
                                       ^
/usr/local/Cellar/octave/4.2.1_6/include/octave-4.2.1/octave/Array.h:360:19: note: 'nelem' has
      been explicitly marked deprecated here
  octave_idx_type nelem (void) const { return numel (); }
                  ^
In file included from __control_slicot_functions__.cc:43:
./sl_ib01cd.cc:97:40: warning: 'nelem' is deprecated [-Wdeprecated-declarations]
        octave_idx_type n_exp = y_cell.nelem ();            // number of experiments
                                       ^
/usr/local/Cellar/octave/4.2.1_6/include/octave-4.2.1/octave/Array.h:360:19: note: 'nelem' has
      been explicitly marked deprecated here
  octave_idx_type nelem (void) const { return numel (); }
                  ^
In file included from __control_slicot_functions__.cc:44:
./sl_ib01ad.cc:148:40: warning: 'nelem' is deprecated [-Wdeprecated-declarations]
        octave_idx_type n_exp = y_cell.nelem ();            // number of experiments
                                       ^
/usr/local/Cellar/octave/4.2.1_6/include/octave-4.2.1/octave/Array.h:360:19: note: 'nelem' has
      been explicitly marked deprecated here
  octave_idx_type nelem (void) const { return numel (); }
                  ^
5 warnings generated.
clang: warning: argument unused during compilation: '-pthread' [-Wunused-command-line-argument]
ld: warning: directory not found for option '-L/usr/local/Cellar/gcc/7.2.0/lib/gcc/7/gcc/x86_64-apple-darwin16.7.0/7.2.0'
ld: warning: directory not found for option '-L/usr/local/Cellar/gcc/7.2.0/lib/gcc/7/gcc/x86_64-apple-darwin16.7.0/7.2.0/../../..'
ld: library not found for -lgfortran
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [__control_slicot_functions__.oct] Error 1
tar -xzf slicot.tar.gz
/usr/local/Cellar/octave/4.2.1_6/bin/mkoctfile-4.2.1 __control_helper_functions__.cc
mkdir sltmp
mv slicot/src/*.f ./sltmp
mv slicot/src_aux/*.f ./sltmp
cp TG04BX.fortran ./sltmp/TG04BX.f
cp TB01ZD.fortran ./sltmp/TB01ZD.f
cd sltmp; /usr/local/Cellar/octave/4.2.1_6/bin/mkoctfile-4.2.1 -c *.f
ar -rc slicotlibrary.a ./sltmp/*.o
rm -rf sltmp slicot
LFLAGS="-L/usr/local/Cellar/octave/4.2.1_6/lib/octave/4.2.1 -L/usr/local/Cellar/octave/4.2.1_6/lib  -L/usr/local/opt/veclibfort/lib -lvecLibFort  -L/usr/local/Cellar/gcc/7.2.0/lib/gcc/7/gcc/x86_64-apple-darwin16.7.0/7.2.0 -L/usr/local/Cellar/gcc/7.2.0/lib/gcc/7/gcc/x86_64-apple-darwin16.7.0/7.2.0/../../.. -lgfortran -lquadmath -lm" \
    /usr/local/Cellar/octave/4.2.1_6/bin/mkoctfile-4.2.1 __control_slicot_functions__.cc common.cc slicotlibrary.a

pkg: error running `make' for the control package.
error: called from
    configure_make at line 95 column 9
    install at line 192 column 7
    pkg at line 394 column 9
```

これは
```
$ mkdir -p /usr/local/Cellar/gcc/7.2.0/lib/gcc/7/gcc/x86_64-apple-darwin16.7.0/7.2.0
```
を実行することで解消できる。

その後、

```
$ octave
octave:1> pkg install -forge signal control  
octave:2> pkg load control
octave:3> pkg load signal
```

を実行することで、tf2zpが使えるようになる。

(参考)
https://github.com/Homebrew/homebrew-science/issues/3167