page_title: Shuffling
section_title: Riffle
hierarchical_section_title: Shuffling / Shuffling techniques / Riffle
caption_attribution_description: English: After a riffle shuffle, the cards cascade.
context_page_description: Shuffling is a procedure used to randomize a deck of playing cards to provide an element of chance in card games. Shuffling is often followed by a cut, to help ensure that the shuffler has not manipulated the outcome.
context_section_description: A common shuffling technique is called the riffle, or dovetail shuffle or leafing the cards, in which half of the deck is held in each hand with the thumbs inward, then cards are released by the thumbs so that they fall to the table interleaved. Many also lift the cards up after a riffle, forming what is called a bridge which puts the cards back into place; it can also be done by placing the halves flat on the table with their rear corners touching, then lifting the back edges with the thumbs while pushing the halves together. While this method is more difficult, it is often used in casinos because it minimizes the risk of exposing cards during the shuffle. There are two types of perfect riffle shuffles: if the top card moves to be second from the top then it is an in shuffle, otherwise it is known as an out shuffle (which preserves both the top and bottom cards).
  The Gilbert–Shannon–Reeds model provides a mathematical model of the random outcomes of riffling, that has been shown experimentally to be a good fit to human shuffling and that forms the basis for a recommendation that card decks be riffled seven times in order to randomize them thoroughly. Later, mathematicians Lloyd M. Trefethen and Lloyd N. Trefethen authored a paper using a tweaked version of the Gilbert-Shannon-Reeds model showing that the minimum number of riffles for total randomization could also be six, if the method of defining randomness is changed.
caption: After a riffle shuffle, the cards cascade
exif: {"Image Make": "EASTMAN KODAK COMPANY", "Image Model": "KODAK P850 ZOOM DIGITAL CAMERA", "Image Orientation": "Horizontal (normal)", "Image XResolution": "230", "Image YResolution": "230", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS Windows", "Image DateTime": "2007:01:25 22:09:38", "Image YCbCrPositioning": "Centered", "Image ExifOffset": "252", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "930", "Thumbnail JPEGInterchangeFormatLength": "5693", "EXIF ExposureTime": "1/80", "EXIF FNumber": "14/5", "EXIF ExposureProgram": "Manual", "EXIF ISOSpeedRatings": "50", "EXIF ExifVersion": "0221", "EXIF DateTimeOriginal": "2007:01:25 14:48:06", "EXIF DateTimeDigitized": "2007:01:25 14:48:06", "EXIF ComponentsConfiguration": "YCbCr", "EXIF ShutterSpeedValue": "633/100", "EXIF ApertureValue": "3", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "3", "EXIF MeteringMode": "Pattern", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash fired, compulsory flash mode", "EXIF FocalLength": "6", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "2592", "EXIF ExifImageLength": "1944", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "EXIF InteroperabilityOffset": "804", "EXIF ExposureIndex": "50", "EXIF SensingMethod": "One-chip color area", "EXIF FileSource": "Digital Camera", "EXIF SceneType": "Directly Photographed", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Manual Exposure", "EXIF WhiteBalance": "Auto", "EXIF DigitalZoomRatio": "0", "EXIF FocalLengthIn35mmFilm": "36", "EXIF SceneCaptureType": "Standard", "EXIF GainControl": "None", "EXIF Contrast": "Hard", "EXIF Saturation": "Normal", "EXIF Sharpness": "Hard", "EXIF SubjectDistanceRange": "1"}