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When the interpolation method is set to LogCubic the iterative bootstrapping may fail during the first two runs. This causes functions that calculate the implied rate or implied index to fail when they are called for the first time.
The user may observe that these functions return properly after they are executed repeatedly several times!
Click on download to download an xml file that contains an Excel formula that demonstrates this issue.
You may then reproduce the issue in spreadsheet by clicking on Go -> Load Excel Formula from XML or one of its variations and choose the xml file downloaded in the step above.