PSAR (Parabolic SAR)

Parabolic SAR (Stop And Reverse) trails price with an accelerating curve. When the indicator flips from above to below price (or vice versa), it signals a potential trend reversal.

Declaration

function init(ctx) {
  ctx.indicator('psar', 'PSAR', { step: 0.02, max: 0.2 });
}

Options

Output

Returns a single number[] series (the SAR value for each bar).

Accessing Values

function onBar(ctx, i) {
  const sar = ctx.ind.psar[i];
  const close = ctx.series.close[i];
  
  // SAR below price = uptrend
  // SAR above price = downtrend
  const isBullish = close > sar;
}

Use Cases

Trend Following

function onBar(ctx, i) {
  const close = ctx.series.close[i];
  const sar = ctx.ind.psar[i];
  const prevSar = ctx.ind.psar[i - 1];
  const prevClose = ctx.series.close[i - 1];
  
  // SAR flipped from above to below price
  if (prevClose <= prevSar && close > sar) {
    ctx.order.market('ASSET', 1, { signal: 'buy', reason: 'psar_bullish' });
  }
  
  // SAR flipped from below to above price
  if (prevClose >= prevSar && close < sar) {
    ctx.order.close('ASSET', { signal: 'sell', reason: 'psar_bearish' });
  }
}

Trailing Stop

function onBar(ctx, i) {
  const sar = ctx.ind.psar[i];
  
  // Use SAR as a dynamic trailing stop level
  if (ctx.position.qty > 0 && ctx.series.close[i] < sar) {
    ctx.order.close('ASSET', { signal: 'sell', reason: 'trailing_stop' });
  }
}

Calculation

The SAR value accelerates toward price using an acceleration factor (AF) that increases by step each bar (up to max) when a new extreme point is reached.

Related

• ADX - Trend strength (pair with PSAR for direction + strength)
• MACD - Momentum-based trend signals
• EMA - Simpler trend-following with moving averages