title: get the last thursday before a date in PHP
body: <p>I know there is similar post about how to get the last Thursday in PHP but I don't want to have the last Thursday compare to the current date but the last Thursday compare to a given date.</p>
  
  <p>For example I have a date dd/mm/yyyy and I want the Thursday before this date.
  The input is a String ( the format of the string yymmdd) that I want to parse to get the Thursday before this date.</p>
  
  <p>Thanks for your help</p>