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极坐标图象
" _. C4 E, @3 Y. y P Matlab中包括一个重要的函数叫做polar,它用于在极坐标系中画图。这个函数的基本形式如下: $ @2 j" f+ X% o
polar(theta,r)
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其是theta代表一个弧度角数组,r代表一个距离数组。它用来画以角度为自变量的函数的极坐标图是非常有用的。
% f" i" E N P7 I+ P- t+ U例3.5
5 k8 x& j7 r1 V D1 L心形麦克风 / O# J1 l# _$ H5 K
为舞台表演设计的麦克风大多都是定向麦克风,它能够增大来自演唱者的信号,抑制后面观众的噪声信号。一个心形麦克风的增益gain是关于角度θ的函数,关系式如下 9 v1 f3 R2 X) z3 o# Y% ]; H
Gain=2g(1+cosθ) (3.3)
+ t% g. w0 I0 {) n9 i9 [& C" e& K其中g是和特定的心形麦克风有关的常量。θ是声源和麦克风之间的夹角。假设一个麦克风的g是0.5,画出函数Gain的极坐标图。 h) b \& O) \& `1 |+ ?. i- I
答案:我们必须计算出与角度对应的函数值,然后画出相应的极坐标图。产生的结果如图3.7所示。注意这种麦克风叫做心形麦克风,所以得出来曲线的形状像颗心。 # w0 ~* v2 |, f+ l- i0 j4 W, y8 U
- O1 ]/ ^ ]7 O$ j9 h+ Rfile:///C:/Users/lx/AppData/Local/Temp/msohtmlclip1/01/clip_image003.gif
/ I9 c! [( O: C' R5 k代码如下:
- t8 U6 a! q# M$ k* O- <div align="left"><font face="Times New Roman"><font color="#000000">% Scriptfile: microphone.m</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">%</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">%Purpose:</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% Thisprogram plots the gain pattern of a cardioid</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% microphone.</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">%</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% Recordof revisions:</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% DateProgrammer Description of change</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% ============== =====================</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% </font></font><font face="Times New Roman"><font color="#000000">12/10/97</font></font><font face="Times New Roman"><font color="#000000">S. J. Chapman Original code</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">%</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% Definevariables:</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% g --Microphone gain constant</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% gain --Gain as a function of angle</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% theta-- Angle from microphone axis (radians)</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">%Calculate gain versus angle</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">g = 0.5;</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">theta =0:pi/20:2*pi;</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">gain =2*g*(1+cos(theta));</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">% Plotgain</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">polar(theta,gain,'r-');</font></font></div><div align="left"><font face="Times New Roman"><font color="#000000">title('Gain versus angle \it\theta');</font></font></div>
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