Forum Discussion
Interpolation in Excel
Hi All, I am hoping someone can help me with an issue I have been having. I am trying to add an Interpolation sum in one of my spreadsheets but I just can't figure out how. Below is the sum: ...
PeterBartholomew1 Thank you Peter for your reply.
I don't actually need the Lookup function as the data will always change, so I would need to manually enter the data anyway.
I tried using your formula but it doesn't give me the answer I need.
It gave the answer you quoted to 6s.f.
That aside, it may go better if you inform the forum of the Excel version you use (my formulation is specific to Excel 365) and ideally provide a workbook to demonstrate how the input is held and the required solution.
That aside, it may go better if you inform the forum of the Excel version you use (my formulation is specific to Excel 365) and ideally provide a workbook to demonstrate how the input is held and the required solution.
PeterBartholomew1 I also use Excel 365.
I'll post an image of the table below:
I hope this makes it easier.
Ultimately I would aim at using a Lambda function to lookup the Room Cavity Ratios but for now
= LET( CU, XLOOKUP(pw₀, pw, table_CU), RCR₁, XLOOKUP(RCR₀,RCR,RCR,,-1), RCR₂, XLOOKUP(RCR₀,RCR,RCR,,1), CU₁, XLOOKUP(RCR₀, RCR, CU,,-1), CU₂, XLOOKUP(RCR₀, RCR, CU,,1), w₁, (RCR₂-RCR₀)/(RCR₂-RCR₁), w₂, (RCR₀-RCR₁)/(RCR₂-RCR₁), IF(RCR₁<>RCR₀, w₁*CU₁+w₂*CU₂, CU₁) )should work with the table as far as I have copied it in to Excel. If you choose to type in the values for RCR₁, RCR₂, CU₁, CU₂, and remove the XLOOKUPS that should work fine, though I would find it tedious and error-prone. Do you also need to interpolate across 'pw' or is that a straight lookup?
- No, the pw only tells you which values to use. I'm basically given a set of data and with this data, I have to find the appropriate values from the table. Then use interpolation to find a more accurate CU value.