Advanced Programming Guide

204 • Chapter 5: Numerical Programming in Maple23 a 2, 2 − 1 3If you call det from inside a call to evalhf, Maple uses the value 0for the unassigned entry, a[2,2].> evalhf( det(a) );−0.333333333333333314evalhf passes arrays by value, so the (2,2) entry of a is still unassigned.> a[2,2];a 2, 2If you want evalhf to modify an array that you pass as a parameterto a procedure, you must enclose the name of the array in a var construct.The var construct is special to evalhf and is necessary only if you wantevalhf to modify an array of numbers that is accessible at the sessionlevel.> evalhf( det( var(a) ) );−0.333333333333333314Now a is an array of floating-point numbers.> eval(a);[0.666666666666666629 , 0.750000000000000000][0.444444444444444420 , 0.]The evalhf command always returns a single floating-point number,but the var construct allows you to calculate a whole array of numberswith one call to evalhf. Section 6.7 illustrates the use of var to calculatea grid of function values for plotting.You can also create arrays of hardware floating-point values directlywith the Array command. Proper use of this command can save significantamounts of time, especially in plotting routines, which rely heavily on