Envelope – EFS

upperEnv(), middleEnv(), lowerEnv() Built-in Study Functions

An envelope is composed of two moving averages. One moving average is shifted upward and the second moving average is shifted downward. Envelopes define the upper and lower boundaries of a security's normal trading range. A sell signal is generated when the security reaches the upper band, whereas a buy signal is generated at the lower band. The optimum percentage shift depends on the volatility of the securitythe more volatile, the larger the percentage.

Syntax

upperEnv( nLength , bExponential , nPercentage [, Series | sym() | inv() ][, nBarIndex ] )

middleEnv( nLength , bExponential , nPercentage [, Series | sym() | inv() ][, nBarIndex ] )

lowerEnv ( nLength , bExponential , nPercentage [, Series | sym() | inv() ][, nBarIndex ] )

Parameters

Parameter:	Description:	Default:
nLength	Required. Number of periods to use for calculation.	n/a
bExponential	Required. Boolean true or false to use exponential calculations.	n/a
nPercentage	Required. Number expressed as a percentage to determin envelope width (i.e. enter 10 for 10%).	n/a
Series or sym() or inv()	[Optional] Series Object or function of sym() or inv() to determine symbol/interval source for the study.	Chart's sym/inv
nBarIndex	[Optional] Bar index of series to retrieve .	n/a

Return Value(s)

Returns a Series Object when nBarIndex is not specified.

Returns a single value when nBarIndex is specified.

Notes

Only available in versions 7.9 or later.

Code Examples

Single Line Indicator:

function main() {
  return new Array(
    upperEnv(20, false, 10),
    middleEnv(20, false, 10),
    lowerEnv(20, false, 10)
  );
}

Single Line Study-on-Study Indicator:

function main() {
  return new Array(
    upperEnv(20, false, 10, hl2()),
    middleEnv(20, false, 10, hl2()),
    lowerEnv(20, false, 10, hl2())
  );
}

Retrieve single values:

function main() {
  var nValue_0 = middleEnv(20, false, 10, 0); // Current Bar Index
  var nValue_1 = middleEnv(20, false, 10, -1); // Prior Bar Index
  return new Array(nValue_0, nValue_1);
}

Initialize Series Objects:

//global Series Object variables
var xStudy1 = null;
var xStudy2 = null;
var xStudy3 = null;
function main() {
  if (xStudy1 == null) xStudy1 = upperEnv(20, false, 10);
  if (xStudy2 == null) xStudy2 = middleEnv(20, false, 10);
  if (xStudy3 == null) xStudy3 = lowerEnv(20, false, 10); // retrieve single values for conditional statements
  var nValue1_0 = xStudy1.getValue(0); // Current Bar Index value
  var nValue2_0 = xStudy2.getValue(0); // Current Bar Index value
  var nValue3_0 = xStudy3.getValue(0); // Current Bar Index value
  var nValue1_1 = xStudy1.getValue(-1); // Prior Bar Index value
  // Plot Current Bar Index Value
  return new Array(nValue1_0, nValue2_0, nValue3_0);
}

Initialize a Series Object based on an external interval:

// global Series Object variables
var xStudy1 = null;
var xStudy2 = null;
var xStudy3 = null;
var bInit = false; // Initialization flag
function main() {
  if (bInit == false) {
    xStudy1 = upperEnv(20, false, 10, inv(20)); // 20-min interval
    xStudy2 = middleEnv(20, false, 10, inv(20)); // 20-min interval
    xStudy3 = lowerEnv(20, false, 10, inv(20)); // 20-min interval
    bInit = true;
  } // retrieve single values for conditional statements
  var nValue1_0 = xStudy1.getValue(0); // Current Bar Index value
  var nValue1_1 = xStudy1.getValue(-1); // Prior Bar Index value
  // Synchronized Series plot
  return new Array(getSeries(xStudy1), getSeries(xStudy2), getSeries(xStudy3));
}

Initialize a Series Object based on an external symbol and interval:

// global Series Object variables
var xStudy1 = null;
var xStudy2 = null;
var xStudy3 = null;
var bInit = false; // Initialization flag
function main() {
  if (bInit == false) {
    xStudy1 = upperEnv(20, false, 10, sym("IBM,20")); // IBM 20-min interval
    xStudy2 = middleEnv(20, false, 10, sym("IBM,20")); // IBM 20-min interval
    xStudy3 = lowerEnv(20, false, 10, sym("IBM,20")); // IBM 20-min interval
    bInit = true;
  } // retrieve single values for conditional statements
  var nValue1_0 = xStudy1.getValue(0); // Current Bar Index value
  var nValue1_1 = xStudy1.getValue(-1); // Prior Bar Index value
  // Synchronized Series plot
  return new Array(getSeries(xStudy1), getSeries(xStudy2), getSeries(xStudy3));
}