# Custom Market Indices
A custom market index is a weighted combination of one or more market indices. Each included index is assigned a percentage weight.
It is not possible to edit any market index values in a custom market index. These are handled entirely by the system.
## The generation of Market Index Values
Consider the custom index above. It is defined as
* 125% of **Market Index 1**
* 33% of **Market Index 2**
* Lumpsum adjustment of **100**
The custom market index derives its values from the market index values of each linked market index. For a given date range, defined by a valid from date and a valid to date, a value is only generated if every linked market index has a market index value covering that exact date range. If any linked market index is missing a value for the date range, no value will be generated for that period.
### Formula
A market index value (C\_MIV) for a custom market index for valid from date (f) and valid to date (t) is generated using the following formula if there exists a market index value (MIV) with the same valid from date and valid to date in **every** market index (MI) that is linked to the custom market index.
$$
\begin{aligned}
C\_MIV^{(f,t)} &= \left(\sum\_{n=1}^{#MI} \left( Frac\_{MI\_n} \cdot MIV\_{MI\_n}^{(f,t)}\right)\right) + \text{lumpsum adjustment} \\
&\text{where } (f,t) = (\text{validFromDate},\ \text{validToDate}) \\
&\text{where } C\_MIV^{(f,t)}= \text{The custom market index value being calculated for }(f,t) \\
&\text{where } #MI = \text{number of market indices in the custom market index} \\
&\text{where } Frac\_{MI\_n} = \text{Percentage}/100 \\
&\text{defined only if } \forall, n \in {1,\dots,#MI},\ \exists, MIV\_{MI\_n}^{(f,t)}
\end{aligned}
$$
### Application of formula
The list on the left is the first 15 market index values from **Market Index 1** and **Market Index 2** on the right.
When the custom market index containing these two market indices is generating its own market index values it groups every market index value by its valid from date and valid to date. This would create a map where 01/01/27 would contain the market index values with value 5800 from Market Index 1 and 8300 from Market Index 2. This goes on until the 25/03/26-25/03/26 market index value, which is a spot value. This date range will only have the market index value form **Market Index 1** with value 5300.
When every market index value has been grouped by valid from date together it discards all entries where the valid from date does not have a market index value from each market index. In our example the 25/03/26-25/03/26 range is discarded.
The remaining entries are then used to generate the actual market index values for the custom market index, where the afformentioned formula is used. Inputing the data for the first entry into the formula it looks like this:
$$
C\_MIV^{(01/01/27,31/12/27)}=(1.25 *5800)+(0.33*8300)+100=10089
$$
The following image is the complete custom market index values generated for the custom market index based on 125% of Market Index 1 and 33% of Market Index 2 with 100 in lumpsum adjustment.
### When market index value are regenerated
The market index values for a custom market is regenerated when the following happens:
* The lumpsum adjustment is changed
* The percentage for one of the market indices is updated
* A market index value on one of the market indices on the custom market index is updated and every market index that is linked to the custom market index has been updated today
* If a custom market index has market index A and B in it, and a market index value on market index A is updated today, but market index B has not been updated today, then the custom market index will not be regenerated by that update. If you then update a market index value on market index B afterwards, then both are updated today, and the market index values on the custom market index will be regenerated.
## Requirements
All market indices in a custom market index must have the same **Unit, Currency, Category.**
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