# Time series properties. Transformations and statistics.

A library of general functions for evaluating statistical and other mathematical
properties of data series (not necessarily prices).

## correl(vars Data, int Length, function): var

Spearman correlation of the **Data** series with an arbitrary
**function**. Used for the CTI,
CCYI, and CCYIR indicators. Source in
**indicators.c**; usage and description on
Financial Hacker.
## Correlation(vars Data1, vars Data2, int TimePeriod): var

Pearson's correlation coefficient between two data series over the given **
TimePeriod**, in the range between **-1..+1**. A coefficient
of +1.0, a "perfect positive correlation," means that changes in
**Data2** cause identical changes in **Data1** (e.g.,
a change in the indicator will result in an identical change in the asset price).
A coefficient of -1.0, a "perfect negative correlation," means that changes
in **Data2** cause identical changes in **Data1**, but
in the opposite direction. A coefficient of zero means there is no relationship
between the two series and that a change in **Data2** will have no
effect on **Data1**. This function can be also used to get the autocorrelation
of a series by calculating the correlation coefficient between the original series
and the same series lagged by one or two bars (**series+1** or
**series+2**).
## Covariance(vars Data1, vars Data2, int TimePeriod): var

Covariance between two data series. Can be used to generate a covariance matrix
f.i. for the markowitz efficient frontier calculation.
## Fisher(vars Data): var

Fisher Transform; transforms a normalized **Data** series to a normal
distributed range. The return value has no theoretical limit, but most values are
between **-1 .. +1**. All **Data** values must be in the
**-1 .. +1** range, f.i. by normalizing with the **AGC**,
**Normalize**, or cdf function. The minimum
**Data** length is **1**; a single **var**
can be passed with the **&** operator, f.i. **
Fisher(&MyVariable).** Source code in **
indicators.c**.
## FisherInv(vars Data): var

Inverse Fisher Transform; compresses the **Data** series to be between
**-1** and **+1**. The minimum length of the **Data**
series is **1**; a single **var** can be passed with
the **&** operator, f.i. **FisherInv(&MyVariable)**. Source
code in **indicators.c**.
## FisherN(vars Data, int TimePeriod): var

Fisher Transform with normalizing; normalizes the **Data** series with
the given **TimePeriod** and then transforms it to a normal distributed
range. Similar to a **Normalize** filter (see below), but more selective
due to the normal distribution of the output. The return value has no theoretical
limit, but most values are in the **-1.5 .. +1.5** range. The minimum
length of the **Data** series is equal to **TimePeriod**.
The function internally creates series and thus must be
called in a fixed order in the script. Source code in **indicators.c**.
## FractalDimension(vars Data, int TimePeriod): var

Fractal dimension of the **Data** series; normally **1..2**.
Smaller values mean more 'jaggies'. Can be used to detect the current market regime
or to adapt moving averages to the fluctuations of a price series. Requires a lookback
period of twice the **TimePeriod**. Source available in **indicators.c**.
## Gauss(vars Data, int TimePeriod): var

Gauss Filter, returns a weighted average of the data within the given time period,
with the weight curve equal to the Gauss Normal Distribution. Useful for removing
noise by smoothing raw data. The minimum length of the **Data** series
is equal to **TimePeriod**, the lag is half the **TimePeriod**.
## Hurst (vars Data, int TimePeriod): var

Hurst exponent of the **Data** series; between **0..1**.
The Hurst exponent measures the 'memory' of a series. It quantifies the autocorrelation,
i.e. the tendency either to revert to the mean (**Hurst < 0.5**)
or to continue trending in a direction (**Hurst > 0.5**). This way
the Hurst exponent can detect if the market is in a trending state. The **
TimePeriod** window (minimum **20**) must have sufficient length
to catch the long-term trend. The function internally creates a
series and thus must be called in a fixed order in the
script. Source available in **indicators.c**.
## LinearReg(vars Data, int TimePeriod): var

Linear Regression, also known as the "least squares moving average"
(LSMA). Linear Regression attempts to fit a straight trendline between several
data points in such a way that the distance between each data point and the trendline
is minimized. For each point, the straight line over the specified previous bar
period is determined in terms of **y = b + m*x**, where **y**
is the price and **x** the bar number starting at **
TimePeriod** bars ago. The formula for calculating **b** and
**m** is then

**m = (nΣxy - ΣxΣy) / (nΣx² - (Σx)²)**

b = (Σy - bΣx)
/ n

where **n** is the number of data points (**TimePeriod**)
and **Σ** is the summation operator. The **LinearReg** function returns **b+m*(TimePeriod-1)**,
i.e. the **y** of the current bar.

**LinearReg** is a
**ta-lib** function. For higher order regression or for evaluating
the regression value at past or future bars, use polyfit / polynom. For logistic
regression with multiple variables, use the advise(PERCEPTRON,...).

## LinearRegAngle(vars Data, int TimePeriod): var

Linear Regression Angle. Returns **m** converted
to degrees. Due to the arbitrary x and y units of a price chart, the angle
is a mostly useless parameter, although held in high esteem by Gann believers.

## LinearRegIntercept(vars Data, int TimePeriod): var

Linear Regression Intercept. Returns **b**.

## LinearRegSlope(vars Data, int TimePeriod): var

Linear Regression Slope. Returns **m** as data difference per bar.

## MaxVal(vars Data, int TimePeriod): var

Highest value over a specified period.

## MaxIndex(vars Data, int TimePeriod): int

Index of highest value over a specified period. **0** = highest value
is at current bar, **1** = at one bar ago, and so on. If the series
was shifted (+N), add the offset **N** to
the returned index for getting the number of bars passed since the lowest
**Data** value.
## Median(vars Data, int TimePeriod): var

Median Filter; sorts the elements of the **Data** series and returns
their middle value within the given time period. Useful for removing noise spikes
by eliminating extreme values. The minimum length of the **Data** series
is equal to **TimePeriod**, the lag is half the **TimePeriod**.
See also Percentile.

## MinVal(vars Data, int TimePeriod): var

Lowest value over a specified period.

## MinIndex(vars Data, int TimePeriod): int

Index of the lowest value over a specified period; **0** = lowest value
is at current bar, **1** = at one bar ago, and so on. If the series
was shifted (+N), add the offset **N** to
the returned index for getting the number of bars passed since the lowest
**Data** value.

## MinMax(vars Data, int TimePeriod): var

Lowest and highest values over a specified period. Result in **rMin**, **rMax**.

## MinMaxIndex(vars Data, int TimePeriod): int

Indexes of lowest and highest values over a specified period. Result in **rMinIdx**,
**rMaxIdx**. **0** = current bar, **1** = one bar ago,
and so on.## Mode(vars Data, int TimePeriod, int Steps): var

Most frequent **Data** value within **TimePeriod**. For
this the **Data** range is divided into **Steps** separate
ranges, and the number of values that fall into a range is counted. The function
returns the value with the highest count.
## Moment(vars Data, int TimePeriod, int N): var

The statistical moment **N** (**1..4**) of the **
Data** series section given by **TimePeriod**. The first moment
is the mean, second is variance, third is skewness, fourth ist kurtosis.
The standard deviation is the square root of the second moment. The mean is
stored in **rMean**. See also **SemiMoment**. Source available
in **indicators.c**.
## Normalize(vars Data, int TimePeriod): var

Transforms the **Data** series to the **-1...+1** range
within the given **TimePeriod**. Similar to the **
AGC** function, but does not differentiate between
attack and decay. The minimum length of the **Data** series is equal
to **TimePeriod**. Source available in **indicators.c**.
See also scale.
## NumInRange(vars Low, vars High, var Min, var Max, int Length): var

Number of data ranges, given by their **Low** and
**High** values, that lie completely inside the interval from
**Min** to **Max** within the given **Length**.
Can be used to calculate the distribution of prices or candles. **Low**
and **High** can be set to the same value for counting
all values in the interval, or swapped for counting all candles that touch the interval.
Returns a value of **1..TimePeriod**. Source available in **indicators.c**.
See also **PercentRank**.
## NumRiseFall(vars Data, int TimePeriod): var

Length of the last streak of rising or falling values in the **Data**
series, back to the given **TimePeriod**. For a rising sequence its
length is returned, for a falling sequence the negative length (f.i. **-3**
when **Data[3] < Data[2] > Data[1] > Data[0]**). Range:
**1..TimePeriod-1**. See the **RandomWalk**
script for an example. Source available in **indicators.c**.
## NumUp(vars Data, int TimePeriod, var Theshold): var

## NumDn(vars Data, int TimePeriod, var Theshold): var

Number of upwards or downwards **Data** changes by more than the given
**Threshold** within the **TimePeriod**, from **
0** to **TimePeriod-1**. See also **SumUp**,
**SumDn**. Source code in **indicators.c**.

## Percentile(vars Data, int Length, var Percent): var

Returns the given percentile of the **Data** series with given
**Length**; f.i. **Percent = 95** returns the **
Data** value that is above 95% of all other values. **Percent = 50**
returns the **Median** of the **Data** series.

## PercentRank(vars Data, int Length, var Value): var

The opposite of **Percentile**: Returns the percentage of **Data**
values within the given **Length** that are smaller or equal than the
given **Value**; returns 100 when** Value **is the greatest
in the data range. Can transform any series to a range of 0..100. See also
**NumInRange**.
## R2(vars Data, int Length): var

Coefficient of determination (+1...-1); similarity of the **Data**
series with a straight line through its end points. At **1** the
data series is equivalent to a straight line, at **0** or below
even the mean of the data is a better fit to the straight line than the real
data series.
## SemiMoment(vars Data, int TimePeriod, int N): var

The statistical moment **N** (**1..4**) of the **
Data** series section given by **TimePeriod**, using only
data points at or below the mean. The first moment
is the mean, the second is the semivariance, third is downside skew, and fourth is
downside kurtosis.
The mean is stored in **rMean**. The **semideviation**
(downside deviation) is the square root of the semivariance, and is often
considered a better measure of risk than the standard deviation. See also
**Moment**. Source available
in **indicators.c**.
## ShannonGain(vars Data, int TimePeriod): var

Expected logarithmic gain rate of the **Data** series in the range
of about **+/-0.0005**. The gain rate is derived from the Shannon probability
**P = (1 + Mean(Gain) / RootMeanSquare(Gain)) / 2**, which is the likeliness
of a rise or fall of a high entropy data series in the next bar period. A positive
gain rate indicates that the series is more likely to rise, a negative gain rate
indicates that it is more likely to fall. The zero crossover could be used for a
trade signal. Algorithm by **John Conover**. Source available in
**indicators.c**.
## ShannonEntropy(vars Data, int Length, int PatternSize): var

Entropy of patterns in the **Data** series, in bit; can be used to
determine the 'randomness' of the data. **PatternSize** (2..8) determines
the partitioning of the data into patterns of up to 8 bit. Each **Data**
value is either higher than the previous value, or it is not; this is a binary information
and constitutes one bit of the pattern. The more random the patterns are distributed,
the higher is the Shannon entropy. Totally random data has a Shannon entropy identical
to the pattern size. Algorithm explained on the
Financial Hacker blog; source available in **indicators.c**.
## Spearman(vars Data, int TimePeriod): var

Spearman's rank correlation coefficient; correlation between the original
**Data** series and the same series sorted in ascending order within
**TimePeriod** (**1..256**). Returns the similarity to
a steadily rising series and can be used to determine trend intensity and turning
points. Range **= -1..+1**, lag = **TimePeriod/2**. For
usage and details, see Stocks & Commodities magazine 2/2011. Source available
in **indicators.c**.

## StdDev(vars Data, int TimePeriod): var

Standard Deviation of the **Data** series in the time period, from
the **ta-lib;** accuracy = **0.0001**. For long time
periods, higher accuracy, or for downside deviation, use the square root of the second
**Moment or SemiMoment**.

## Sum(vars Data, int TimePeriod): var

Sum of all **Data** elements in the time period.
## SumUp(vars Data, int TimePeriod): var

## SumDn(vars Data, int TimePeriod): var

Sum of all upwards or downwards **Data** changes within the **
TimePeriod**. See also **NumUp**, **NumDn**. Source
code in **indicators.c**.

## TSF(vars Data, int TimePeriod): var

Time Series Forecast. Returns **b + m*(TimePeriod)**, the Linear Regression
forecast for the next bar.

## Variance(vars Data, int TimePeriod): var

Variance of the **Data** series in the time period, from the
**ta-lib; **accuracy = **0.0001.** For long time
periods, higher accuracy, or for downside variance, use the second
**Moment or SemiMoment**.

### Standard parameters:

**TimePeriod ** |
The number of bars for the time period of the function, if any; or
**0** for using a default period. |

**Length ** |
The length of the **Data** series. |

**Data** |
A data series, often directly derived from
the price functions **price(), priceClose()**
etc.. Alternatively a user created series or any other double float array
with the given minimum length can be used. If not mentioned otherwise, the
minimum length of the **Data** series is **TimePeriod**.
Some functions require a second data array **Data2**. |

### Usage example:

**Volatility(Prices,20)** calculates the standard volatility of a daily
price series over the last 20 days.
### Remarks:

- The
**TA-Lib** function prototypes are defined in **include\functions.h**.
Information about the usage and the indicator algorithms can be found online
at www.tadoc.org. The C source
code of all included TA-Lib indicators is contained in **Source\ta_lib.zip**
and can be studied for examining the algorithms. Some TA-Lib indicators that
originally didn't work properly - such as Correlation or SAR - have been replaced
by working versions. The C source code of most additional indicators that are
not part the the TA-Lib is contained in **Source\indicators.c**.
- All TA functions are applied on series and do normally
not accept other data arrays. In the INITRUN, all TA functions
return
**0**, and LookBack is automatically
increased to the largest required lookback time by a TA function.
- TimeFrame affects subsequent data
series and thus also affects all indicators that use
the data series as input. The
**TimePeriod** is then not in Bar
units, but in time frame units. **TimeFrame** has no effect on
indicators that do not use data series.

### Examples:

*// plot some indicators*
function run()
{
set(PLOTNOW);*
* var* Price = series(price());

*// plot Bollinger bands
* BBands(Price,30,2,2,MAType_SMA);

plot("Bollinger1",rRealUpperBand,BAND1,0x00CC00);

plot("Bollinger2",rRealLowerBand,BAND2,0xCC00FF00);

plot("SAR",SAR(0.02,0.02,0.2),DOT,RED);

ZigZag(Price,20*PIP,5,BLUE);

*// plot some other indicators *

plot("ATR (PIP)",ATR(20)/PIP,NEW,RED);

plot("Doji",CDLDoji(),NEW+BARS,BLUE);

plot("FractalDim",FractalDimension(Price,30),NEW,RED);

plot("ShannonGain",ShannonGain(Price,40),NEW,RED);

}

### See also:

Spectral filters, indicators,
normalization, candle patterns,
machine learning
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