54 lines
3.5 KiB
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54 lines
3.5 KiB
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<TITLE>CLHS: Constant Variable PI</TITLE>
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<A NAME="pi"><I>Constant Variable</I> <B>PI</B></A> <P>
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<P><B>Value:</B><P>
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<P>
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an <A REL=DEFINITION HREF="26_glo_i.htm#implementation-dependent"><I>implementation-dependent</I></A> <A REL=DEFINITION HREF="26_glo_l.htm#long_float"><I>long float</I></A>. <P>
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<P><B>Description:</B><P>
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<P>
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The best <A REL=DEFINITION HREF="26_glo_l.htm#long_float"><I>long float</I></A> approximation to the mathematical constant <PI>. <P>
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<P><B>Examples:</B><P>
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<P>
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<PRE>
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;; In each of the following computations, the precision depends
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;; on the implementation. Also, if `long float' is treated by
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;; the implementation as equivalent to some other float format
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;; (e.g., `double float') the exponent marker might be the marker
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;; for that equivalent (e.g., `D' instead of `L').
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pi => 3.141592653589793L0
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(cos pi) => -1.0L0
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(defun sin-of-degrees (degrees)
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(let ((x (if (floatp degrees) degrees (float degrees pi))))
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(sin (* x (/ (float pi x) 180)))))
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</PRE>
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</TT> <P>
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<P><B>See Also:</B> None.
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<P>
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<P><B>Notes:</B><P>
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<P>
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An approximation to <PI> in some other precision can be obtained by writing <TT>(float pi x)</TT>, where <TT>x</TT> is a <A REL=DEFINITION HREF="26_glo_f.htm#float"><I>float</I></A> of the desired precision, or by writing <TT>(coerce pi </TT><I>type</I><TT>)</TT>, where <I>type</I> is the desired type, such as <A REL=DEFINITION HREF="t_short_.htm#short-float"><B>short-float</B></A>. <P>
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