blitz_2.html

A C++ class library for scientific computing

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<H3> 2.1.4 Storage orders </H3>
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<P>

Blitz++ is very flexible about the way arrays are stored in memory.
</P><P>

The default storage format is row-major, C-style arrays whose indices start
at zero.
</P><P>

Fortran-style arrays can also be created.  Fortran arrays are stored in
column-major order, and have indices which start at one.  To create a
Fortran-style array, use this syntax: <CODE>Array&#60;int,2&#62; A(3, 3,
fortranArray);</CODE> The last parameter, <CODE>fortranArray</CODE>, tells the
<CODE>Array</CODE> constructor to use a fortran-style array format.  
</P><P>

<CODE>fortranArray</CODE> is a global object which has an automatic conversion to
type <CODE>GeneralArrayStorage&#60;N&#62;</CODE>.  <CODE>GeneralArrayStorage&#60;N&#62;</CODE>
encapsulates information about how an array is laid out in memory.  By
altering the contents of a <CODE>GeneralArrayStorage&#60;N&#62;</CODE> object, you can lay
out your arrays any way you want: the dimensions can be ordered arbitrarily
and stored in ascending or descending order, and the starting indices can be
arbitrary.
</P><P>

Creating custom array storage formats is described in a later section
(<A HREF="blitz_2.html#SEC68">2.9 Array storage orders</A>).
</P><P>

<A NAME="Array types"></A>
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<H2> 2.2 Public types </H2>
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The <CODE>Array</CODE> class declares these public types:
</P><P>

<UL>

<LI><CODE>T_numtype</CODE> is the element type stored in the array.  For
example, the type <CODE>Array&#60;double,2&#62;::T_numtype</CODE> would be <CODE>double</CODE>.
<P>

<LI><CODE>T_index</CODE> is a vector index into the array.  The class
<CODE>TinyVector</CODE> is used for this purpose.
<P>

<LI><CODE>T_array</CODE> is the array type itself
(<CODE>Array&#60;T_numtype,N_rank&#62;</CODE>)
<P>

<LI><CODE>T_iterator</CODE> is an iterator type.  NB: this iterator is not
yet fully implemented, and is NOT STL compatible at the present time.
<P>

</UL>
<P>

<A NAME="Array ctors"></A>
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<H2> 2.3 Constructors </H2>
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<H3> 2.3.1 Default constructor </H3>
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<P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>Array();
Array(GeneralArrayStorage&#60;N_rank&#62; storage)
</pre></td></tr></table></P><P>

The default constructor creates a C-style array of zero size.  Any attempt
to access data in the array may result in a run-time error, because there
isn't any data to access!
</P><P>

An optional argument specifies a storage order for the array.
</P><P>

Arrays created using the default constructor can subsequently be given data
by the <CODE>resize()</CODE>, <CODE>resizeAndPreserve()</CODE>, or <CODE>reference()</CODE>
member functions.
</P><P>

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<H3> 2.3.2 Creating an array from an expression </H3>
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<TABLE><tr><td>&nbsp;</td><td class=example><pre>Array(expression...)
</pre></td></tr></table></P><P>

You may create an array from an array expression.  For example,
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>Array&#60;float,2&#62; A(4,3), B(4,3);   // ...
Array&#60;float,2&#62; C(A*2.0+B);
</pre></td></tr></table></P><P>

This is an explicit constructor (it will not be used to perform implicit
type conversions).  The newly constructed array will have the same storage
format as the arrays in the expression.  If arrays with different storage
formats appear in the expression, an error will result.  (In this case, you
must first construct the array, then assign the expression to it).
</P><P>

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<H3> 2.3.3 Constructors which take extent parameters </H3>
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<TABLE><tr><td>&nbsp;</td><td class=example><pre>Array(int extent1);
Array(int extent1, int extent2);
Array(int extent1, int extent2, int extent3);
...
Array(int extent1, int extent2, int extent3, ..., int extent11)
</pre></td></tr></table></P><P>

These constructors take arguments which specify the size of the array to be
constructed.  You should provide as many arguments as there are dimensions
in the array.<A NAME="DOCF1" HREF="blitz_fot.html#FOOT1">(1)</A>
</P><P>

An optional last parameter specifies a storage format:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>Array(int extent1, GeneralArrayStorage&#60;N_rank&#62; storage);
Array(int extent1, int extent2, GeneralArrayStorage&#60;N_rank&#62; storage);
...
</pre></td></tr></table></P><P>

For high-rank arrays, it may be convenient to use this constructor:
<A NAME="IDX24"></A>
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>Array(const TinyVector&#60;int, N_rank&#62;&#38; extent);
Array(const TinyVector&#60;int, N_rank&#62;&#38; extent, 
      GeneralArrayStorage&#60;N_rank&#62; storage);
</pre></td></tr></table></P><P>

The argument <CODE>extent</CODE> is a vector containing the extent (length) of the
array in each dimension.  The optional second parameter indicates a storage
format.  Note that you can construct <CODE>TinyVector&#60;int,N&#62;</CODE> objects on the
fly with the <CODE>shape(i1,i2,...)</CODE> global function.  For example,
<CODE>Array&#60;int,2&#62; A(shape(3,5))</CODE> will create a 3x5 array.
</P><P>

A similar constructor lets you provide both a vector of base index values
(lbounds) and extents:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>Array(const TinyVector&#60;int, N_rank&#62;&#38; lbound, 
      const TinyVector&#60;int, N_rank&#62;&#38; extent);
Array(const TinyVector&#60;int, N_rank&#62;&#38; lbound,
      const TinyVector&#60;int, N_rank&#62;&#38; extent,
      GeneralArrayStorage&#60;N_rank&#62; storage);
</pre></td></tr></table></P><P>

The argument <CODE>lbound</CODE> is a vector containing the base index value (or
lbound) of the array in each dimension.  The argument <CODE>extent</CODE> is a
vector containing the extent (length) of the array in each dimension.  The
optional third parameter indicates a storage format.  As with the above
constructor, you can use the <CODE>shape(i1,i2,...)</CODE> global function to
create the <CODE>lbound</CODE> and <CODE>extent</CODE> parameters.
</P><P>

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<H3> 2.3.4 Constructors with Range arguments </H3>
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<P>

These constructors allow arbitrary bases (starting indices) to be set:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>Array(Range r1);
Array(Range r1, Range r2);
Array(Range r1, Range r2, Range r3);
...
Array(Range r1, Range r2, Range r3, ..., Range r11);
</pre></td></tr></table></P><P>

For example, this code:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>Array&#60;int,2&#62; A(Range(10,20), Range(20,30));
</pre></td></tr></table></P><P>

will create an 11x11 array whose indices are 10..20 and 20..30.  An optional
last parameter provides a storage order:
</P><P>

<TABLE><tr><td>&nbsp;</td><td class=example><pre>Array(Range r1, GeneralArrayStorage&#60;N_rank&#62; storage);
Array(Range r1, Range r2, GeneralArrayStorage&#60;N_rank&#62; storage);