it is for regression class so have a lot of math symbol like this
$$\mathbf{X^TX}=
\left[\begin{array}
& 1 &1 &...&1 \
x_1& x_2 &...& x_n
\end{array}\right]
\left[\begin{array}
& 1 &x_1 \
1 &x_1\
.&.\
.&.\
1&x_n
\end{array}\right]
this is the error
Error: Failed to compile early_test.tex.
In addition: Warning message:
In system2(..., stdout = FALSE, stderr = FALSE) : '"pdflatex"' not found
Execution halted
No TeX installation detected (TeX is required to create PDF output). You should install a recommended TeX distribution for your platform:
Windows: MiKTeX (Complete) - http://miktex.org/2.9/setup
(NOTE: Be sure to download the Complete rather than Basic installation)
Mac OS X: TexLive 2013 (Full) - http://tug.org/mactex/
(NOTE: Download with Safari rather than Chrome strongly recommended)
Linux: Use system package manager