如何将一条线拟合到变换中的数据子部分？

我有一点时间将线性拟合应用于一小块数据（目标是提取vt，ala Baker 3rd Ed。p 293中显示的方法）。
我有一个gm vs Vgs的图，我尝试过类似于fit_line演示中显示的变换，但它似乎确实理解限制了特定范围值的拟合。
这是我的转换中的代码，试图从vgs值2.3到4.3 V的线性拟合gm数据：gm = DERIVAtiVE2（vg.m，id.m，1，-1）OVERRIDE_LIMITS =“Y”X_LOW
= 2.3 X_HIGH = 4.3 fit = fit_line（vg.m，gm，1，-1）RETURN fit我也尝试在Setup Variables选项卡中定义X_LOW和X_HIGH，也没有运气。
我也尝试过linfit功能。
有什么建议么？
谢谢，Paul *编辑修复错别字*编辑：Paul Shepherd于2014年4月9日上午7:42



     以下为原文

  I am having a heck of a time applying a linear fit to a small region of data (the goal is to extract vt, ala the method shown in Baker 3rd Ed. p 293).

I have a plot of gm vs Vgs, and I have tried making transforms similar to the ones shown in the fit_line demo, but it just does seem to understand limiting the fit to a specific range of values. Here is my code in my transform to try to get a linear fit to the gm data from vgs values of 2.3 to 4.3 V:

gm = DERIVATIVE2(vg.m, id.m, 1, -1)
OVERRIDE_LIMITS = "Y"
X_LOW=2.3
X_HIGH=4.3
fit = fit_line(vg.m     , gm, 1, -1)
RETURN fit

I have tried defining X_LOW and X_HIGH in the Setup Variables tab as well, also with no luck. I have also tried the linfit function.

Any suggestions?

Thanks,
Paul

*edited to fix typos*

Edited by: Paul Shepherd on Apr 9, 2014 7:42 AM