The force index by Dr. Alexander Elder shows daily close-to-close changes multiplied by the volume traded, so that moves on greater volume are given more significance. The raw change*volume values are smoothed slightly with a 2-day EMA (see Exponential Moving Average), so the formula is simply
Force Index = EMA of (volume * (close - prev close))
An increasing force index indicates strong interest in an upward move, when it falls back either price or volume or both have declined suggesting waning interest. Conversely for a negative and falling force index on the downside. The smoothing period for the EMA is configurable.
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