The Fortran committee botched DO CONCURRENT badly. The requirements imposed on the program only make it safe to execute its iterations in any serial order, but are not sufficient to allow safe parallel execution. So one can write a perfectly conforming DO CONCURRENT loop that will produce wrong answers when actually run in parallel. The problem in the spec seems to have been inadvertent but they have refused to fix it (and don’t seem to understand the problem either.)
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The Fortran committee botched DO CONCURRENT badly. The requirements imposed on the program only make it safe to execute its iterations in any serial order, but are not sufficient to allow safe parallel execution. So one can write a perfectly conforming DO CONCURRENT loop that will produce wrong answers when actually run in parallel. The problem in the spec seems to have been inadvertent but they have refused to fix it (and don’t seem to understand the problem either.)