CBCGPChartTrendFormula

Detailed Description

The CBCGPChartTrendFormula class calculates coefficients for trend lines of different types. When a Trend Formula object is attached to a series, the series is drawn as a non-discrete curve on the diagram.

A Trend Formula object allows to specify only one input series. Then, depending on selected approximation type, it calculates coefficients using data points from the input series and generates screen positions for a non-discrete curve.

Currently the following trend lines are supported:

• Linear (y = a * x + b)
• Exponential (y = a * exp(b*x))
• Power (y = a * pow (x, b))
• Logarithmic (y = a * log(x) + b)
• Polynomial of order n = [2 - 6] (y = kn * x ^ n + kn-1 * x ^ (n - 1) + ... + k0)

The following picture illustrates a polynomial trend line of order 3:

If you don't specify the input series, you can set your custom coefficients (AddCoefficient()) and display a curve calculated using the formulas above.

You can override CalculateTrendCoefficients() and OnCalculateYValue() methods to implement custom formulas.

The following code displays a polynomial trend line of order 3:

Copy

CBCGPChartVisualObject* pChart = m_wndChart.GetChart();

CBCGPChartSeries* pInputSeries = pChart->CreateSeries(_T("Input Series"));

// ... add data points to input series

CBCGPChartSeries* pSeriesResult = pChart->CreateSeries(_T("Trend Line"));

// set polynomial type

CBCGPChartTrendFormula formula((CBCGPChartTrendFormula::TLT_POLYNOMIAL);

// set input series

formula.SetInputSeries(pInputSeries);

// set polynomial trend order

formula.SetPolynomialTrendOrder(3);

pSeriesResult->SetFormula(formula);

You can display a trend line on predefined range using SetTrendRange(). Call GetFormulaText() to retrieve a string with the formula text.

Note. After a formula object has been added to a series, you must use CBCGPChartSeries::GetFormula to obtain a pointer to the formula and modify it.

See also

CBCGPChartBaseFormula