4)由Matlab符号运算得到的公式怎么才能将数据代进去运算?
:#ramjet (德芙)2002/3/3, SMTH/MathTools #
使用subs(),或先将值赋予一个符号变量,然后用eval()
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5)在Matlab中如何求最值点?如何求一维数组的极值?
:#FangQ(Qianqian.3710167@qq.com),2002/6/18, SMTH/MathTools#
最值:
一维或多维数组最值用max(data(:))
如果想返回最值所在的位置,用[Y,I]=max(data)
:#FangQ(Qianqian.3710167@qq.com), 2001/4/21,UESTC/Math#
极值:
data是你的数据,
find(diff(sign(diff(data)))==-2)+1
找到极大值的位置
find(diff(sign(diff(data)))==2)+1
找到极小值的位置
data(find(diff(sign(diff(data)))==-2)+1)和
data(find(diff(sign(diff(data)))==2)+1)
返回的是极大值和极小值
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6)Matlab中如何作线性拟合/线性回归/多元线性回归?
:#FangQ(Qianqian.3710167@qq.com),2002/6/21, BigGreen/MathTools #
即用y=a*x+b来拟合一组数据{{x1,y1},{x2,y2}…{xn,yn}}
matlab中使用polyfit
x=data(:,1);
y=data(:,2);
p=polyfit(x,y,1);
p(1)为斜率a,p(2)为截距b
多元线性回归即用y=a1*x1+a2*x2+..+am*xm来拟合数据点{x1i,x2i,…xmi,yi}
(i=1~n)
|x11,x21,…xm1|
A=|x12,x22,…xm2|
|…………… |
|x1n,x2n,…xmn|
Y={y1,y2,y3,…,yn}'
则系数{a1,a2,…,am}'=pinv(A)*Y
在matlab中使用
coeff=A\Y
则可以得到最小二乘意义上的拟合系数
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7)Matlab中如何作圆回归?
:#Peter Boettcher (3710167@qq.com.edu),2002/5/16, comp.soft-sys.matlab#
Q5.5: How can I fit a circle to a set of XY data?
=================================================
An elegant chunk of code to perform least-squares circle fitting
was written by Bucher Izhak and has been floating around the
newgroup for some time. The first reference to it that I can
find is in:
function [xc,yc,R,a] = circfit(x,y)
%CIRCFIT Fits a circle in x,y plane
%
% [XC, YC, R, A] = CIRCFIT(X,Y)
% Result is center point (yc,xc) and radius R.A is an
% optional output describing the circle's equation:
%
% x^2+y^2+a(1)*x+a(2)*y+a(3)=0
% by Bucher izhak 25/oct/1991
n=length(x); xx=x.*x; yy=y.*y; xy=x.*y;
A=[sum(x) sum(y) n;sum(xy) sum(yy)...
sum(y);sum(xx) sum(xy) sum(x)];
B=[-sum(xx+yy) ; -sum(xx.*y+yy.*y) ; -sum(xx.*x+xy.*y)];
a=A\B;
xc = -.5*a(1);
yc = -.5*a(2);
R = sqrt((a(1)^2+a(2)^2)/4-a(3));
Tom Davis provided a more sophisticated approach that works
for more cases in and Code included.
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8)Matlab中如何绘制箭头?
:#FangQ(Qianqian.3710167@qq.com),2002/6/21, SMTH/MathTools #
到mathworks/matlabcentral/fileexchange/index.jsp
2-D Plotting and Graphics中查找arrow.m,或者
mathworks/matlabcentral/spotlight/arrows.shtml
math.umd.edu/~jec/matcomp/matcompmfiles/mfiles.html
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9)Matlab中如何作二维数据的插值?
:#FangQ(Qianqian.3710167@qq.com),2002/6/21, BigGreen/MathTools #
对于一维、二维、三维规则数据点阵使用interp1/interp2/interp3,
二维、三维非规则数据用griddata/griddata3
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10)Matlab中如何绘制三维数据阵?
:#FangQ(Qianqian.3710167@qq.com),2002/6/21, BigGreen/MathTools #
如果使用matlab,打开帮助窗口,在目录树上找到
MATLAB\Using Matlab\
3-D Visualization: Volume Visualization Techniques
如果图形复杂,建议使用Tecplot,参