## Calculations

A: If you are using two calculated columns to make a diagram they must be created in the same calculation window at the same time rather than by two separate calculations.  This is the way the program has been designed and the reason behind this is that as each of the variables is assigned a term, eg. A, B, C, etc which is used in the calculated expression.  If there is more than calculation file then it would be possible to have duplicate terms being used in which reference different variables. Eg. A = SiO2% in the first calculation but A = Al2O3% in the second calculation.  This information is all stored in the underlying XML and within the ioGAS file so by having all the calculations done together each variable is assigned a unique term.

A. If an input column in a calculated expression contains 0′s then when the calculation is run the calculated column will report blanks for the 0 entries. A red warning is displayed down in the status bar that the Selected data contains Infinite Values. This warning is also displayed when the calculated column is selected in the Select Variables dialog. To prevent an empty plot window from opening try one of the following options:

1. Select the variables containing null values in the Select Variables dialog and then use the Validate>Data Doctor menu option prior to calculating the column to convert the 0 values to null. The XY plots will then display the remaining valid data.
2. If the calculated column is already created,  attribute all of the blank records in the tabular data view with a colour and then make this colour group invisible in the Attribute Manager. When the XY plot is calculated all of the other valid data points now plot.
3. Clean data prior to import

A. If you wanted to add 1 to all sample values over 100 ppm (and leave all sample values < 100 as 0) for example then the syntax would be along the lines of:

Input Column = Cu_ppm = A

Expression: If (A>100,A+1,0)

The If statement has three components:

• The selection expression: eg. A>100

• The result if not 0: eg. A+1

• The if 0: eg. 0

A. If an input column in an expression contains null data then no results will be calculated for any output columns for the null records.  This is regardless of whether the input column is used in the calculated expression for that column but only when working in Multivariate mode.  Multivariate mode requires that records must contain a valid data value for all input columns otherwise the output columns will record null values.  To enable the calculations to run independently of each other uncheck the Multivariate mode box so that univariate mode is used.

A: Fe analyses may be reported either as total iron or as explicit ferrous (Fe2+) or ferric (Fe3+) values.  Sometimes Fe data must be in a specific format before samples can be used in a calculation.  To make sure that ioGAS uses the correct column values the following aliases are available:

·       Fe – Total Fe

·       Fe2O3 – Total ferric (3+) oxide

·       FeO – Total ferrous (2+) oxide

·       Fe2O3* – Explicit ferric (3+) oxide

·       FeO* – Explicit ferrous (2+) oxide

Calculations which require an Fe component in most cases will have a (Total Iron) and an explicit (Fe2+_Fe3+) version to choose from.  The (Total Iron) version requires one of Fe, Fe2O3 or FeO to be aliased.  The (Fe2+_Fe3+) version requires two Fe columns of data to be aliased to Fe2O3* and FeO* otherwise the calculation or diagram will be greyed out.

It is possible to calculate explicit Fe2+ or Fe3+ values from total Fe values (and vice versa) using a variety of methods, some of which can be found under the Calculations menu.  Use these calculations to converted data into the correct Fe format required.

A: Converting from Ca_pct to CaO_pct:

1. Make sure that Ca_pct is aliased in the Data>Column Properties dialog

2. Select Calculation>New Geochem Calculation

3. In the Input Columns drop-down list see how CaO_pct is bolded as well as Ca_pct. Even if you only have Ca_pct in your dataset all of the bolded elements are ones that ioGAS can automatically convert between as it knows your input element/units column. So, from the Input Columns list choose CaO_pct

5. If you don’t want to use the CaO_pct column in another expression remove the Output Columns line using the MINUS button on the right hand side

6. Check the Make Input Columns box

7. Click Calculate All and the CaO_pct column should be added to your dataset.

A: This can be explained using an example. I have 4 columns: P_ppm, Ti_ppm, P2O5_pct and TiO2_pct. The first two columns (P_ppm and Ti_ppm) have data in all rows. Most of the rows in the last two columns (P2O5 and TiO2) are empty, with some cells containing values. I want to populate the remaining cells in the last two columns using Make Input Columns in Create New Geochem Calculation, and by selecting P2O5 and TiO2 as the input columns. However, no values were created to fill the empty cells in P2O5 and TiO2.

The overriding principle with element conversion in ioGAS is that it won’t run calculation to create something that already exists. In this case, the conversion will not create any values for columns P2O5 and TiO2, because ioGAS assumes that the existing values are correct. If the original columns for P2O5 and TiO2 are renamed (e.g. to P2O5_pct_ and TiO2_pct_), then the columns for P2O5 and TiO2 will be populated with values. However, if the original columns for P2O5 and TiO2 are removed, ioGAS will recalculate the columns.