In v3.2.0 of the C++ ITensor library, we have removed the function format from the itensor:: namespace in favor of explicitly calling it with tinyformat::format. The reason is to remove a conflict with the std::format function, available in C++20.

If your code uses the format function, please call tinyformat::format from now on instead if you'd like to call exactly the same function (tinyformat is the underlying library supplying this function). You can optionally use a shorthand such as tfm::format by adding namespace tfm = tinyformat; to your code. Alternatively, you can update your code to use std::format.