Script runs, but can't see solution

Question

Kelly McGuire 2017-4-4

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/333668-script-runs-but-can-t-see-solution

评论： Star Strider 2017-4-5

matlabPic.jpg

My code is shown below. I am trying to fit my data with an equation we developed. I get a plot at the end of the run with no errors, but all I see is the data curve, no fitting curve. What could be wrong here? I've attached the figure that is produced when running this script. The data is in blue, and the fitting curve should show up in red...VarName1 and VarName2 are the x and y data points I imported.

t = VarName1;
y = VarName2;
plot(x,y,'--b');
xlabel('Time');
ylabel('Current');
modelFun = @(p,t)(-167.*((1 - (p(2) ./ p(1).*(0.0001 - ((4 .* 0.0001 / 3.1415)) .* (exp(-((1/20) .*...
    (3.1415^2) .* t ./ 1000))-(1/3) .* exp(-((9/20) .* (3.1415^2) .* t ./ 1000)...
    )) / 3.1415))) .* exp(-((p(1) .* (0.0001 - ((4 .* 0.0001 / 3.1415) .* (exp(-((1/20) .* (3.1415^2)...
    .* t ./ 1000))-(1/3) .* exp(-((9/20) .* (3.1415^2) .* t ./ 1000))) / 3.1415)...
    )) + p(2)) .* t ./ 1000)+(p(2) ./ p(1) .* (0.0001 - ((4 .* 0.0001 / 3.1415) .* (exp(-((1/20).*...
    (3.1415^2) .* t ./ 1000))-(1/3) .* exp(-((9/20) .* (3.1415^2) .* t / 1000)...
    )) / 3.1415)) + p(2))));
startingVals = [-296 0.0573];
coefEsts = nlinfit(t, y ,modelFun, startingVals);
xgrid = linspace(0,20,100);
line(xgrid, modelFun(coefEsts, xgrid), 'Color', 'r');

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Joseph Cheng 2017-4-5

what do you get when you just plot(xgrid, modelFun(coefEsts, xgrid), 'Color', 'r');

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Star Strider 2017-4-5

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/333668-script-runs-but-can-t-see-solution#answer_261782

You defined your independent variable ‘xgrid’ to go from 0 to 20, while ‘t’ goes from 0 to 3.5E+5. When I define ‘xgrid’ to match ‘t’, the plot of your function looks like the data in the image you posted.

What did you intend to plot?

2 个评论
显示无隐藏无

Kelly McGuire 2017-4-5

Thanks, that worked. One more question, how do I get the curve to fit only the data and not extrapolate beyond the curve (initially and at the end)?

Star Strider 2017-4-5

My pleasure.

I’m not certain what values ‘t’ has, so I would use it as the independent variable. That should keep the fitted curve from extrapolating beyond the region of fit at the high end.

The beginning (near 0) you can either leave alone, or manually define the time where the curve begins to increase as the beginning, using the plot GUI ‘Data Cursor’ to find it. I don’t know enough about your data to figure a way to do that programmatically. It looks like the maximum deviations from the fitted curve are at the beginning, so you might use that as a criterion. I don’t know how well your curve fits your data to be certain that would be a reliable technique.

请先登录，再进行评论。