Linear regression : How to take into account the quadratic term only and not the linear term ?

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Emile Belot
Emile Belot 2022-4-22
回答： Star Strider 2022-4-22
Hello everyone,
I am currently working on a linear regression using the fitlm tool. I collect my datas from a table name "newT2" that has 3 columns.
Here is my code :
modelaction = 'Var1 ~ Var2 + Var3^2';
mdlaction = fitlm(newT2, modelaction);
The problem is that the regression is done according this equation : 'Var1 ~ Var2 + Var3+ Var3^2'. But it's not what I asked, I don't want the linear term Var3.
In fact, if I run with the equation 'Var1 ~ Var2 + Var3^3', the regression is done according : 'Var1 ~ Var2 + Var3+ Var3^2 + Var3^3' and so on.
Thanks for your help !

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回答（1 个）

Star Strider
Star Strider 2022-4-22
Ran in:
Suppress the intercept term and the linear ‘Var3’ by negating them —
newT2 = array2table(rand(7,3)) % Create Data Table
newT2 = 7×3 table
Var1 Var2 Var3 _______ _______ ________ 0.9339 0.56678 0.7716 0.86767 0.18461 0.039493 0.95488 0.51097 0.95676 0.53864 0.8246 0.86486 0.23089 0.41095 0.76704 0.93338 0.12252 0.19638 0.91871 0.38145 0.6025
modelaction = 'Var1 ~ - 1 + Var2 - Var3 + Var3^2'; % Specify Model
mdlaction = fitlm(newT2, modelaction)
mdlaction =
Linear regression model: Var1 ~ Var2 + Var3^2 Estimated Coefficients: Estimate SE tStat pValue ________ ______ ________ _______ Var2 1.7668 1.4213 1.2431 0.26895 Var3^2 -0.38241 1.2132 -0.31521 0.76534 Number of observations: 7, Error degrees of freedom: 5 Root Mean Squared Error: 0.572
.

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