Why does LinearModelFit give me an equation in $z$ rather than $x$?

Question

I am working on a Mathematica notebook and making graphs for my lab. I can't make a graph for my linearized data as LinearModelFit gives equation in z even though I pass x as an argument.

linfit = LinearModelFit[data, x, x]

Answer 1

Somewhere/sometime before LinearModelFit[data,x,x] is invoked you must have defined x as z. To check if this is the case you can use ValueQ:

ValueQ[x]

gives True if a value has been defined for x, and gives False otherwise. Alternatively, you can use

?x

which returns

if x is previously assigned a value, just the first line otherwise.

The following simple examples replicates your case:

x = z;
data = {{0, 1}, {1, 0}, {3, 2}, {5, 4}};
linfit = LinearModelFit[data, x, x]

As a fix, you can use ClearAll to clear all values, definitions, attributes, messages, and defaults associated with x before using x in LinearModelFit:

ClearAll[x]
linfit = LinearModelFit[data, x, x]