# An align environment error

I have an issue to run the following code in an align environment:

\begin{align}
\mathbf{D}^{(m)} = \mathbf{D} \mathbf{D} \cdots \mathbf{D} =  \mathbf{D}^m,\quad \boldsymbol{f}^{(m)} = \mathbf{D}^{(m)} \boldsymbol{f}
\end{align}


The error message shows me the following:
"Package inputenc Error: Invalid UTF-8 byte 168. fractional advection� "

Where is the problem?

• Welcome to TeX.SE. Please provide a full MWE. Sep 17 at 2:35
• There is a possibility that a non-printing unicode character slipped into your input. If you have narrowed it down to this block of code, consider retyping the equation in from scratch. FYI, when I copy and paste this code into a document, it works just fine. Sep 17 at 2:39
• A separate question: Why do you use an align environment, which is meant to be used for multi-line displayed equations, for what appears to be a single line of displayed math? Put differently, why don't you use an equation environment?
– Mico
Sep 17 at 5:55
• I don't think that the equation you show is responsible for the error, which instead refers to some text part, after an appearance of the word advection. Sep 17 at 8:58
• @Steven B. Segletes: Thank you for your help! The problem was solved when I added this statement (\UserawInputEncoding) at the beginning of the article. Sep 18 at 2:24