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@victorlei
victorlei committed Sep 6, 2014
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Expand Up @@ -9,25 +9,86 @@ contains the necessary runtime support -- several class
definitions and about 30 small everyday functions, such
as ``length``.

This matlab program ``solver.m`` was taken from the matlab
programming competition in 2004 (Moving Furniture). To the
right is ``a.py`` -- its SMOP translation to python.
Example: ``solver.m``
The matlab program ``solver.m`` was taken from the matlab
programming competition in 2004 (Moving Furniture). To the
right is ``a.py`` -- its SMOP translation to python.
Though only 30 lines long, this example shows many of
the complexities of converting matlab code to python.


.. code:: matlab
01 function mv = solver(ai,af,w) 01 def solver_(ai,af,w,nargout=1):
02 nBlocks = max(ai(:)); 02 nBlocks=max_(ai[:])
03 [m,n] = size(ai); 03 m,n=size_(ai,nargout=2)
==== ========================================================
02 Matlab uses round brackets both for array indexing and
for function calls. To figure out which is which,
SMOP computes local use-def information, and then
applies the following rule: undefined names are
functions, while defined are arrays.
---- --------------------------------------------------------
03 Matlab function ``size`` returns variable number of
return values, which corresponds to returning a tuple
in python. Since python functions are unaware of the
expected number of return values, their number must be
explicitly passed in ``nargout``.
==== ========================================================

.. code:: matlab
04 I = [0 1 0 -1]; 04 I=matlabarray([0,1,0,- 1])
05 J = [1 0 -1 0]; 05 J=matlabarray([1,0,- 1,0])
06 a = ai; 06 a=copy_(ai)
07 mv = []; 07 mv=matlabarray([])
==== ========================================================
04 Matlab array indexing starts with one; python indexing
starts with zero. New class ``matlabarray`` derives from
``ndarray``, but exposes matlab array behaviour. For
example, ``matlabarray`` instances always have at least
two dimensions -- the shape of ``I`` and ``J`` is [1 4].
---- --------------------------------------------------------
06 Matlab array assignment implies copying; python
assignment implies data sharing. We use explicit copy
here.
---- --------------------------------------------------------
07 Empty ``matlabarray`` object is created, and then
extended at line 28. Extending arrays by
out-of-bounds assignment is deprecated in matlab, but
is widely used never the less. Python ``ndarray``
can't be resized except in some special cases.
Instances of ``matlabarray`` can be resized except
where it is too expensive.
==== ========================================================

.. code:: matlab
08 while ~isequal(af,a) 08 while not isequal_(af,a):
09 bid = ceil(rand()*nBlocks); 09 bid=ceil_(rand_() * nBlocks)
09 bid = ceil(rand*nBlocks); 09 bid=ceil_(rand_() * nBlocks)
10 [i,j] = find(a==bid); 10 i,j=find_(a == bid,nargout=2)
11 r = ceil(rand()*4); 11 r=ceil_(rand_() * 4)
11 r = ceil(rand*4); 11 r=ceil_(rand_() * 4)
12 ni = i + I(r); 12 ni=i + I[r]
13 nj = j + J(r); 13 nj=j + J[r]
==== ========================================================
09 Matlab functions of zero arguments, such as
``rand``, can be used without parentheses. In python,
parentheses are required. To detect such cases, used
but undefined variables are assumed to be functions.
---- --------------------------------------------------------
10 The expected number of return values from the matlab
function ``find`` is explicitly passed in ``nargout``.
---- --------------------------------------------------------
12 Variables I and J contain instances of the new class
``matlabarray``, which among other features uses one
based array indexing.
==== ========================================================

.. code:: matlab
14 if (ni<1) || (ni>m) || 14 if (ni < 1) or (ni > m) or
(nj<1) || (nj>n) (nj < 1) or (nj > n):
15 continue 15 continue
Expand All @@ -38,7 +99,7 @@ right is ``a.py`` -- its SMOP translation to python.
20 [ti,tj] = find(af==bid); 20 ti,tj=find_(af == bid,nargout=2)
21 d = (ti-i)^2 + (tj-j)^2; 21 d=(ti - i) ** 2 + (tj - j) ** 2
22 dn = (ti-ni)^2 + (tj-nj)^2; 22 dn=(ti - ni) ** 2 + (tj - nj) ** 2
23 if (d<dn) && (rand()>0.05) 23 if (d < dn) and (rand_() > 0.05):
23 if (d<dn) && (rand>0.05) 23 if (d < dn) and (rand_() > 0.05):
24 continue 24 continue
25 end 25
26 a(ni,nj) = bid; 26 a[ni,nj]=bid
Expand All @@ -47,45 +108,6 @@ right is ``a.py`` -- its SMOP translation to python.
29 end 29
30 30 return mv
Though only 30 lines long, this example shows many of
the complexities of converting matlab code to python.

==== ========================================================
line
==== ========================================================
02 Matlab uses round brackets both for array indexing and
for function calls. To figure out which is which,
SMOP computes local use-def information, and then
applies the following rule: undefined names are
functions; defined, are arrays.
---- --------------------------------------------------------
03 Matlab function ``size`` returns variable number of
return values. In python, functions are usually unaware
of the expected number of return values. To solve this,
number of return values is explicitly passed in
``nargout``.
---- --------------------------------------------------------
04 Matlab array indexing starts with 1, python starts with
zero. New class matlabarray derives from ndarray, but
exposes matlab array behaviour.
---- --------------------------------------------------------
06 Matlab array assignment implies copying; python
assignment implies data sharing. We use explicit copy
here.
---- --------------------------------------------------------
07 Empty matlabarray object is created, and then extended
at line 28.
---- --------------------------------------------------------
09 Matlab functions of zero arguments can be used without
the parentheses, such as ``rand``.
---- --------------------------------------------------------
10 Matlab function ``find`` returns variable number
of values, which is explicitly passed in `nargout`.
---- --------------------------------------------------------
12 Variables I and J contain matlab-style arrays.
==== ========================================================

Command-line options
--------------------

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