请问你这段程序中st=[320740.5];320740.5是如何确定的?>>y=[556,632,745,755,769,789,985,1110,1313,1428,1782,1920,2150,2292,2601,3149,4338,5145,5809,6241,6854,7656,8772,10007,11374,12567,14332,16614,19228,22844,26404,29688,32074]';x=[

Question

请问你这段程序中st_ = [32074 0.5]; 32074 0.5是如何确定的?
>> y=[556,632,745,755,769,789,985,1110,1313,1428,1782,1920,2150,2292,2601,3149,4338,5145,5809,6241,6854,7656,8772,10007,11374,12567,14332,16614,19228,22844,26404,29688,32074]';
x=[1978:1:2010]';
st_ = [32074 0.5];
ft_ = fittype('a/(1+(a/556-1)*exp(-b*(x-1978))) ' ,...
'dependent',{'y'},'independent',{'x'},...
'coefficients',{'a','b'});
[cf_ ,good]= fit(x,y,ft_ ,'Startpoint',st_)
h_ = plot(cf_,'fit',0.95);
legend off; % turn off legend from plot method call
set(h_(1),'Color',[1 0 0],...
'LineStyle','-','LineWidth',2,...
'Marker','none','MarkerSize',6);
hold on,plot(x,y,'*')
cf_ =
General model:
cf_(x) = a/(1+(a/556-1)*exp(-b*(x-1978)))
Coefficients (with 95% confidence bounds):
a = 2.654e+007 (-1.936e+009,1.989e+009)
b = 0.1273 (0.1249,0.1296)
good =
sse:7.581000406528857e+006
rsquare:0.997101925993753
dfe:31
adjrsquare:0.997008439735487
rmse:4.945183517429948e+002

Answer 1

st_ = [32074 0.5];
32074 0.5分别是a和b的初值,根据方程式的含义大概估计的
a应该是人口上限 b增长率